PREGNANCY AND BIRTHS CONTRACTED PELVIS

PREGNANCY AND BIRTHS CONTRACTED PELVIS. MACROSOMIA IN OBSTETRICS, PREGNANCY AND DELIVERY. MULTIFETAL GESTATION.

Prepared by I. Kuziv

 Any contraction of the pelvic diameters that diminishes the capacity of the pelvis can create dystocia during labor. Pelvic contractions may be classified as follows:

1.  Contraction of the pelvic inlet

2.  Contraction of the midpelvis

3.  Contraction of the pelvic outlet

4.  Generally contracted pelvis (combinations of the above)

CONTRACTED PELVIC INLET

Definition.    The  pelvic inlet is usually considered to be contracted if its shortest anteroposterior diameter is less than 10.0 cm or if the greatest transverse diameter is less than 12.0 cm. The anteroposterior diameter of the pelvic inlet is commonly approximated by manually measuring the diagonal conjugate, which is about 1.5 cm greater. Therefore,  inlet contraction is usually defined as a diagonal conjugate of less than 11.5 cm. The errors inherent in the use of this clinical measurement are discussed in Chapter 3.

Using clinical and, at times, imaging pelvimetry, it is important to identify the shortest anteroposterior diameter through which the fetal head must pass. Occasionally, the body of the first sacral vertebra is displaced forward so that the shortest distance may actually be between this false, or abnormal, sacral promontory and the symphysis pubis.

Prior to labor, the  fetal biparietal diameter has been shown to average from 9.5 to as much as 9.8 cm in different populations. Therefore, it might prove difficult or even impossible for some fetuses to pass through an inlet with an anteroposterior diameter of less than 10 cm. Mengert (1948) and Kaltreider (1952), employing x-ray pelvimetry, demonstrated that the incidence of difficult deliveries is increased to a similar degree when either the anteroposterior diameter is less than 10 cm or the transverse diameter of the inlet is less than 12 cm. When both diameters are contracted, dystocia is much greater than when only one is contracted. The configuration of the pelvic inlet is also an important determinant of the adequacy of any pelvis, independent of actual measurements of the anteroposterior and transverse diameters and of calculated “areas”

A small woman is likely to have a small pelvis, but she is also likely to have a small infant. Thoms (1937) studied 362 nulliparas and found the mean birthweight of their offspring was significantly lower (280 g) in women with small pelves than in those with medium or large pelves. In veterinary obstetrics, it has frequently been observed that in most species maternal size rather than paternal size is the important determinant of fetal size.

FETAL PRESENTATION AND POSITION

Fetal Presentation and Position.    A contracted inlet plays an important part in the production of abnormal presentations. In normal nulliparas, the presenting part at term commonly descends into the pelvic cavity before the onset of labor. When the inlet is contracted considerably, however, descent usually does not take place until after the onset of labor, if at all. Cephalic presentations still predominate, but because the head floats freely over the pelvic inlet or rests more laterally in one of the iliac fossae, very slight influences may cause the fetus to assume other presentations.  In women with contracted pelves, face and shoulder presentations are encountered three times more frequently, and cord prolapse occurs four to six times more frequently. Critchlow and colleagues (1994) have quantified the magnitude of risk for cord prolapse in women with cephalopelvic disproportion.

COURSE OF LABOR

Course of Labor.    When a pelvic deformity is sufficiently severe to prevent the head from entering the inlet, labor is prolonged and effective spontaneous labor is often never achieved.

MATERNAL EFFECTS

    Although maternal and fetal effects resulting from inlet contraction are divided arbitrarily in the following discussion, bony dystocia may result in serious consequences to either or both patients.

ABNORMALITIES IN CERVICAL DILATATION

 Abnormalities in Cervical Dilatation.    Normally, cervical dilatation is facilitated by hydrostatic action of the unruptured membranes or, after their rupture, by direct application of the presenting part against the cervix. In contracted pelves, however, when the head is arrested in the pelvic inlet, the entire force exerted by the uterus acts directly upon the portion of membranes that overlie the dilating cervix. Consequently, early spontaneous rupture of the membranes is more likely to result.

After membrane rupture, the absence of pressure by the head against the cervix and lower uterine segment predisposes to less effective contractions. Hence, further dilatation may proceed very slowly or not at all. Cibils and Hendricks (1965) reported that the mechanical adaptation of the fetal passenger to the bony passage plays an important part in determining the efficiency of contractions. The better the adaptation, the more efficient are the contractions. Because adaptation is poor in the presence of a contracted pelvis, prolongation of labor often results. With degrees of pelvic contractions incompatible with vaginal delivery, the cervix seldom dilates satisfactorily. Thus, cervical response to labor provides a prognostic view of the outcome of labor in women with inlet contraction.

MANAGEMENT

    For inlet contraction, management is determined principally by the prognosis for safe vaginal delivery. If, on the basis of the criteria reviewed, a delivery that is safe for both mother and child cannot be anticipated, cesarean delivery is indicated. Only in a minority of instances can a prognosis be reached before the onset of labor. A carefully managed trial of labor is desirable in most instances. Women with inlet contractions are particularly likely to have both weak uterine contractions during first-stage labor and a need for vigorous voluntary expulsive efforts during the second stage. Therefore, the use of conduction analgesia should in general be approached with caution. The course of labor should be monitored closely and the prognosis established as soon as reasonably possible. With greater parity, the likelihood of uterine rupture increases. Finally, oxytocin administration in the presence of any known form of pelvic contraction, unless the fetal head has unequivocally passed the point of obstruction, can be catastrophic.

CONTRACTED MIDPELVIS

Definition.    The obstetrical plane of the midpelvis extends from the inferior margin of the symphysis pubis, through the ischial spines, and touches the sacrum near the junction of the fourth and fifth vertebrae. A transverse line theoretically connecting the ischial spines divides the midpelvis into anterior and posterior portions. The former is bounded anteriorly by the lower border of the symphysis pubis and laterally by the ischiopubic rami. The posterior portion is bounded dorsally by the sacrum and laterally by the sacrospinous ligaments, forming the lower limits of the sacrosciatic notch.

 Average midpelvis measurements are as follows: transverse (interspinous), 10.5 cm; anteroposterior (from the lower border of the symphysis pubis to the junction of the fourth and fifth sacral vertebrae), 11.5 cm;  and posterior sagittal (from the midpoint of the interspinous line to the same point on the sacrum), 5 cm. Although the definition of midpelvic contractions has not been established with the same precision possible for inlet contractions,  the midpelvis is likely contracted when the sum of the interischial spinous and posterior sagittal diameters of the midpelvis (normally, 10.5 plus 5 cm, or 15.5 cm) falls to 13.5 cm or below. This concept has been emphasized by Chen and Huang (1982) in evaluating possible midpelvic contraction. There is reason to suspect midpelvic contraction whenever the interischial spinous diameter is less than 10 cm. When it is smaller than 8 cm, the midpelvis is contracted. The preceding definitions of midpelvic contraction do not, of course, imply that dystocia will necessarily occur in such a pelvis, but simply that it more likely will develop. Development of dystocia also depends upon the size and shape of the forepelvis and the size of the fetal head, as well as on the overall degree of midpelvic contraction.

IDENTIFICATION

Identification.    Although there is no precise manual method of measuring midpelvic dimensions, a suggestion of contraction can sometimes be inferred if the spines are prominent, the pelvic side walls converge, or the sacrosciatic notch is narrow. Moreover, Eller and Mengert (1947) pointed out that the relationship between the intertuberous and interspinous diameters of the ischium is sufficiently constant that narrowing of the interspinous diameter can be anticipated when the intertuberous diameter is narrow. A normal intertuberous diameter, however, does not always exclude a narrow interspinous diameter .

PROGNOSIS

 Midpelvic contraction is probably more common than inlet contraction, and it is frequently a cause of transverse arrest of the fetal head. This can potentially lead to difficult midforceps operation or to cesarean delivery.

MANAGEMENT

   The natural forces of labor should be allowed to push the biparietal diameter beyond the potential interspinous obstruction. Forceps operations may be very difficult when applied to a head whose greatest diameter has not yet passed a contracted midpelvis. This difficulty may be explained on two grounds: (1) pulling on the head with forceps destroys flexion, whereas pressure from above increases it; and (2) although the forceps blades occupy a space of only a few millimeters, the blades further diminish available space. Only when the head has descended to such an extent that the perineum is bulging and the vertex is actually visible is it reasonably certain that the head has passed the obstruction. It is then usually safe to apply forceps. Strong fundal pressure should not be used in attempts to force the head past the obstruction.

The use of forceps to affect delivery in midpelvic contraction, usually undiagnosed, has been responsible for much of the stigma attached to midforceps operations. Thus, midforceps should not be attempted if there is reasonable evidence for midpelvic contraction and the fetal biparietal diameter has not passed beyond the level of contraction.

The vacuum extractor  has been reported to be of advantage in some cases of midpelvic contraction after the cervix has become fully dilated. Traction need not cause deflection of the fetal head, and the vacuum extractor does not occupy space, as do forceps. As with forceps, however, the vacuum extractor should not be applied unless the biparietal diameter has passed the pelvic obstruction. Oxytocin, of course, has no place in the treatment of known dystocia caused by midpelvic contraction.

CONTRACTED PELVIC OUTLET

Definition and Incidence

    Contraction of the pelvic outlet is usually defined as diminution of the interischial tuberous diameter to 8 cm or less. The pelvic outlet may be roughly likened to two triangles  

The interischial tuberous diameter constitutes the base of both. The sides of the anterior triangle are the pubic rami, and its apex the inferior posterior surface of the symphysis pubis. The posterior triangle has no bony sides but is limited at its apex by the tip of the last sacral vertebra (not the tip of the coccyx). Floberg and associates (1987) reported that outlet contractions were found in almost 1 percent of over 1400 unselected term nulliparas.

 Maternal Position.    Recently, considerable interest has been shown in alternative second-stage labor birth positions. Gupta and co-workers (1991) reported that several randomized controlled trials, with and without the use of specific birthing aids, have produced conflicting results and are confounded by observer bias. One reported advantage from avoiding the traditional lithotomy position is an increase in the dimensions of the pelvic outlet. Specifically, Russell (1969) described a 20 to 30 percent increase in the area of the pelvic outlet with squatting compared with the supine position. Gupta and co-workers (1991) compared the usual Western delivery position (recumbent with the head and shoulders up 30 degrees) with the squatting position and found no significant change in the dimensions of either the pelvic inlet or outlet. Crowley and associates (1991) randomized 634 women to deliver in an obstetrical birth chair and compared these with 596 women delivered in bed. There were no advantages with use of the birthing chair, but hemorrhage was increased in this group.

Ambulation during labor has also not been shown to be advantageous. MacLennan and colleagues (1994) randomized 196 women in spontaneous labor at term to ambulation or the recumbent position. Interestingly, 60 percent of women randomized to ambulation declined to do so when active labor ensued despite encouragement to comply. No advantages were attributed to ambulation in the remaining women who complied with ambulation.

Immersion of laboring women in water has been advocated as a means of relaxation that may contribute to more efficient labor (Odent, 1983). Schorn and colleagues (1993) randomized 96 women with term gestations to immersion in a hot tub with air jets or their prevailing labor management. The women were permitted to stay in the tub as long as they desired, and most stayed 30 to 45 minutes. Water immersion did not alter the rate of cervical dilation, length of labor, route of delivery, or analgesia use. Walker (1994) and Alderdice and associates (1995) have reviewed this subject.

PROGNOSIS

    It is apparent from Figure   that diminution in the intertuberous diameter with consequent narrowing of the anterior triangle must inevitably force the fetal head posteriorly. Whether delivery can take place therefore partly depends on the size of the posterior triangle, or more specifically on the interischial tuberous diameter and the posterior sagittal diameter of the outlet. A contracted outlet may cause dystocia not so much by itself as through the often associated midpelvic contraction. Outlet contraction without concomitant midplane contraction is rare.

RARE PELVIC CONTRACTIONS

Due to the relative safety of cesarean delivery, rare pelvic contractions do not result in the same maternal and fetal consequences as in earlier times. Therefore, the descriptions and illustrations of these many and varied pelvic contractions have been omitted (). Potentially lethal problems other than pelvic abnormalities may be encountered in dwarfs and in women with poliomyelitis or  kyphoscoliosis, and in those who are small and dysmorphic. These dangers include, but are not limited to pulmonary and cardiovascular abnormalities

ESTIMATING FETAL HEAD SIZE AND PELVIC CAPACITY

Clinical, radiological, and ultrasonic techniques have been used with varying degrees of success to determine the size of the fetal head as well as the dimensions of the bony pelvis and their relationship.

FETAL HEAD SIZE

Clinical Estimation.    Impression of the fetal head into the pelvis, as described by Mьller (1880) and Hillis (1930), may provide useful information. In an occiput presentation, the brow and the suboccipital region are grasped through the abdominal wall with the fingers and firm pressure is directed downward in the axis of the inlet. Fundal pressure by an assistant usually is helpful. The effect of the forces on the descent of the head can be evaluated by palpation with a sterile gloved hand in the vagina. If no disproportion exists, the head readily enters the pelvis, and vaginal delivery can be predicted. Inability to push the head into the pelvis, however, does not necessarily indicate that vaginal delivery is impossible. A clear demonstration of a flexed fetal head that overrides the symphysis pubis, however, is presumptive evidence of disproportion. Thorp and colleagues (1993) performed a prospective evaluation of the Mueller-Hillis maneuver and concluded that there was no relation between dystocia and failure of descent of the head.

 

Figure 1.   Adult female pelvis. Anteroposterior (AP) and transverse (T) diameters of the pelvic inlet are illustrated, as well as the posterior sagittal of the inlet.

 

 

 

Figure 2.   Pelvic outlet with diameters marked. Note that the anteroposterior diameter may be divided into anterior and posterior sagittal diameters.

 

Figure 3.   The four parent pelvic types of the Caldwell–Moloy classification. A line passing through the widest transverse diameter divides the inlet into posterior (P) and anterior (A) segments.

MACROSOMIA

  Macrosomia is a term used rather imprecisely to describe a very large fetus/newborn. There is general agreement among obstetricians that newborns weighing less than 4000 g are not excessively large; but a similar consensus has not been reached that permits a precise definition of macrosomia. In the contemporary literature, newborn weights greater than 4000, 4100, or 4500 g (10 pounds) have been suggested as appropriate to define macrosomia (Boyd and colleagues 1983; Modenlau and colleagues 1980; Neiger, 1992). There is no doubt that fetuses who are born weighing 4500 to 5000 g are at less risk of a poor perinatal outcome than those who weigh more than 5000 g (Spellacy and co-workers, 1985). But even within a group of large fetuses of a rather restricted weight range, neonatal outcome with macrosomia can be affected by the presence or absence of compounding variables (e.g., maternal diabetes). Among macrosomic fetuses of diabetic women, for example, there is a greater shoulder circumference and a greater shoulder circumference-to-head circumference ratio, and consequently, a greater risk of shoulder dystocia, compared with fetuses of similar body weight of nondiabetic women (Modenlau and colleagues, 1982; Neiger, 1992; Sachs, 1993). Among macrosomic fetuses of similar body weight, the presence of a relatively greater proportion of body fat tissue is associated independently with an increased risk of labor dystocia and, in consequence, cesarean delivery (Bernstein and Catalano, 1994). For these reasons, and in the absence of a commonly agreed-upon definition of macrosomia, a generally accepted obstetrical management plan optimal for this pregnancy complication has not evolved.

Based on ultrasonic measurements of the fetus, some relatively complex computations have been proposed to identify macrosomia:  the ponderal index, 100 times the body weight of the infant divided by the cube of its length; or the symmetry index, the ratio between newborn length and weight, each divided by the length and weight of the population’s 50th percentile (Keller and associates, 1990; Sachs, 1993; Walther and Ramaekers, 1982).  The American College of Obstetricians and Gynecologists (1991) concluded that the term “macrosomia” was an appropriate designation for fetuses who, at birth, weigh 4500 g or more.

RISK FACTORS

Maternal diabetes, obesity, or both are the most important of known risk factors for development of fetal macrosomia. There are several other factors, however, that also favor the likelihood of a large fetus: (1) large size of the parents, especially the mother; (2) multiparity; (3) prolonged gestation; (4) male fetus; (5) previous delivery of an infant weighing more than 4000 g; (6) smoking status of the mother; and (7) race and ethnicity (Benito and co-workers, 1996; Chervenak, 1992; Johnson and co-workers, 1992; Perlow and associates, 1992; Sachs, 1993). When the pregnant woman weighs more than 300 pounds, her fetus is at greater risk of macrosomia (30 percent) or, conversely, growth retardation (8 percent). Among women who are simultaneously diabetic, obese, and postterm, the incidence of fetal macrosomia can range from 5 to 15 percent (Arias, 1987; Chervenak, 1992). Known maternal risk factors, however, are identified in only 40 percent of women who deliver macrosomic fetuses (Boyd and associates, 1983).

INCIDENCE OF MACROSOMIA

There are wide variations in mean birthweights of various peoples of the world, to wit: 2400 g among the Lumi of New Guinea, but 3830 g among the native American Cheyenne Indians (Meredith, 1970; Sachs, 1993). In the Obstetrical Statistical Cooperative study of more than 104,000 deliveries, 5.3 percent of the newborns weighed more than 4000 g, but only 0.4 percent weighed more than 4500 g. Among the more than 15,000 deliveries at Parkland Hospital in 1991, 7.7 percent of the newborns weighed 4000 g or more but only approximately 1 percent weighed more than 4500 g (Ramin and Cunningham, 1995). These data are noteworthy because this obstetrical population is comprised of predominantly young women who often are socioeconomically deprived and present with a relatively low prevalence of diabetes. Moreover, the incidence of excessively large babies in each of the birthweight groups cited in this population has increased during the past two decades.

The excessively large newborn is still a curiosity. Newborn weight rarely exceeds 11 pounds (5000 g). Indeed, the birth of a 16-pound (7300 g) infant in the United States in 1979 was widely publicized; delayed maternal glucose metabolism was identified, and this woman previously had delivered several infants weighing 9 to 10 pounds. Two of the largest newborn weights ever recorded were that of a nearly 24-pound (10,800 g) infant, as described by Beach in 1879 (Barnes, 1957), and a 25-pound stillborn cited in Chapter 5.  There were only 23 newborns who weighed 5000 g or more (1.5 per 1000 births) delivered in Parkland Hospital in 1991. Among approximately 74,000 infants who were delivered at this institution between 1987 and 1991, only two weighed 6000 g or more, an incidence of 2.7 per 100,000 deliveries. The larger of these two infants, 6065 g (13 lb 51¤2 oz), was delivered by cesarean section (Fig. 37–1 ); but the other, 6050 g, was delivered per vagina without complications.

DIAGNOSIS

 Presently, an accurate estimate of excessive fetal size (weight) is not possible; consequently, the diagnosis of macrosomia most commonly is not made until after the fetus is delivered. Inaccuracy in clinical estimates of fetal weight by physical examination is often attributable, at least in part, to maternal obesity.

Numerous attempts have been made to improve the accuracy of fetal weight estimations by analyses of various measurements obtained by ultrasonography. A number of formulas have been proposed for analyses using ultrasonic measurements of fetal head, femur, and abdomen to estimate fetal weight. The estimates provided by these computations are reasonably accurate for predicting the weight of small, preterm fetuses; but using this approach, estimates of fetal weight with very large fetuses are not as reliable. The relationship between actual and predicted newborn weight, using the most commonly applied formulas proposed by Shepard and co-workers (1982) and Watson and Seeds (1991), are presented in Table 37–1.  Among fetuses estimated to weigh more than 4000 g or more than 4500 g, the probability that the actual birthweight would correspond with that predicted was only 50 percent. In another study of more than 300 fetuses who, at birth weighed in excess of 4000 g, Benacerraf and co-workers (1988) found a sensitivity of predictability of only 65 percent. These investigators were able to exclude 90 percent of fetuses as not having macrosomia, but because 90 percent of term newborns weigh less than 4000 g, this prediction is not particularly useful. Pollack and colleagues (1992), in a study confined to postterm pregnancies, used a formula (with ultrasonic measurements) proposed by Hadlock and associates (1984) to estimate fetal weight. The measurements applied to this formula were the abdominal circumference and the femur length. They found that only half of fetuses with macrosomia—greater than 4000 g—were correctly identified, and that only 65 percent of the fetuses that were predicted to be macrosomic actually weighed more than 4000 g at birth. These investigators deduced that to achieve 70 percent confidence that the actual birthweight would be greater than 4000 g, the estimated fetal weight must be greater than 4750 g. Similar findings and conclusions were presented by Chervenak and associates (1989) and Combs and co-workers (1993). In a comparison of the accuracy of fetal weight estimates made from computations with three different formulas (using sonographic measurements), Miller and colleagues (1987) found that the positive predictive value of macrosomia by these several estimates was 60 percent or less. O’Reilly-Green (1996) studied 202 consecutive postterm pregnancies and found a positive predictive value of 79 percent for 4000 g but only 33 percent for 4500 g.

Other sonographic measurements for use in estimating the weight of the fetus who may have macrosomia have been proposed: chest circumference, femur length/abdominal circumference ratio, soft-tissue thickness of the proximal humerus or femur, thickness of fetal abdominal fat line, and cheek-to-cheek diameter (Abramowicz, 1993; Miller, 1987; Mintz, 1989; Petrikovsky, 1996; Santolaya-Forgas, 1994, and their colleagues).

Unfortunately, a formula that gives estimates of fetal macrosomia with sufficiently accurate predictive value to be useful in constructing clinical management decisions has not been derived or evaluated (American College of Obstetricians and Gynecologists, 1991). In a comprehensive review of estimates of fetal weight from ultrasonic measurements to identify macrosomia, Sandmire (1993) argued that the use of such data in clinical decision making may cause more harm than good. He suggested that a moratorium be placed on the reporting and clinical use of sonographic data in estimates of excess fetal weight. Indeed, Adashek and colleagues (1996) found that women who had ultrasonography in the last 4 weeks of pregnancy were at significantly increased risk for cesarean delivery if estimated fetal size exceeded 4000 g, regardless of actual newborn weight.

We conclude that the estimation of fetal weight from ultrasonic measurements is not proven to be reliable. Nonetheless, sonographic measurements to evaluate excess fetal weight to assist in clinical management decisions may be warranted in rare circumstances. Routine use of these estimates to identify macrosomia are not recommended; indeed, the findings of several studies are indictive that estimates of fetal weight by physician-conducted physical examination of the pregnant woman are as reliable as, or even superior to, those made from ultrasonic fetal measurements (Chauhan and colleagues, 1992, 1993; Hanretty and co-workers, 1990; Sandmire, 1993; Watson and associates, 1988). Chauhan and associates (1992) suggested that the parous woman in labor at term can herself predict fetal weight with a degree of accuracy comparable to that predicted by physician examination or by ultrasonographic measurements!

COMPLICATIONS OF MACROSOMIA

The accurate estimation of fetal weight in pregnancies in which a macrosomic fetus is suspected could prove useful for two reasons.

Fetopelvic Disproportion with Macrosomia.    Knowledge of fetal weight might permit the avoidance of vaginal delivery of pregnancies in which labor most likely would be arrested because of true fetopelvic disproportion. Unfortunately, however, even with a very accurate prediction of fetal weight, variations in size and shape of the maternal pelvis, variable effects of soft tissue on the course of labor, or flexibility of the joints of the pelvic girdle would not be taken into account. The diagnosis of cephalopelvic disproportion often cannot be established by any criteria other than the outcome of an adequate trial of labor (American College of Obstetricians and Gynecologists, 1989). Labor itself, however, is unlikely to cause harm to the macrosomic fetus or the mother in a carefully managed pregnancy that ultimately must be delivered by cesarean section because of arrest of labor.

SHOULDER DYSTOCIA WITH MACROSOMIA

.    Fetal shoulder dystocia, and the attendant risk of permanent brachial plexus palsy, in pregnancies with a macrosomic fetus is cause for considerable concern. Shoulder dystocia occurs when the maternal pelvis is of sufficient size to permit delivery of the fetal head, but not large enough to allow delivery of the very large-diameter fetal shoulders. In this circumstance, the anterior shoulder becomes impacted against the maternal symphysis pubis (Chap. 42 ); and even with expert obstetrical assistance at delivery, stretching and injury of the brachial plexus of the affected shoulder may be inevitable. It must be recognized, however, that the risk of brachial plexus injury is increased substantially when inappropriate force is applied during attempts to complete vaginal delivery (Allen and co-workers, 1994). Only 30 percent of all brachial plexus injuries caused by shoulder dystocia are sustained by infants who weigh more than 4000 g (Walle and Hartkainen-Sorri, 1993). Nevertheless, the relative risk of this complication is appreciably greater with macrosomic fetuses; and it is very likely that some of these injuries could be avoided if cesarean delivery were elected.

On the one hand, therefore, the prospective identification of fetuses at risk for macrosomia and shoulder dystocia is a desirable goal. But on the other hand, the success of management plans that include cesarean delivery for macrosomia (based upon estimates of fetal size) is highly dependent on the precision of the estimations of fetal weight to predict brachial plexus injury. Otherwise, the greater maternal morbidity that accrues with operative deliveries is not justified. As emphasized by Sandmire (1993), clavicular fracture and cephalohematoma do not cause long-term disabilities; consequently, strict avoidance of these complications may not be sufficiently warranted to justify the obliged increase in cesarean deliveries. Fortunately, 95 percent of brachial plexus palsies are transient (Gordon and associates, 1973); but unfortunately, a significant proportion of brachial plexus impairments occur in non-macrosomic infants, or else are not caused directly by shoulder dystocia.

 Some obstetricians have suggested that cesarean delivery should be elected when the fetus is estimated to weigh in excess of 4000 or 4250 g in pregnancies of diabetic women, or 4500 g in pregnancies of nondiabetic women. Data in support of this proposal (i.e., a documented reduction in the incidence of permanent brachial plexus palsy or other birth injury resulting from the implementation of this management plan), however, has not been provided (Acker and associates, 1985; Langer and colleagues, 1991; Sandmire, 1993; Spellacy and co-workers, 1985). Even assuming that the weight of macrosomic fetuses could be estimated accurately, obligatory cesarean delivery based on specific, but arbitrarily chosen, fetal weight thresholds would result in many unnecessary operations. Consider the following: at Parkland Hospital in 1991, 1162 infants weighing 4000 g or more were delivered; of these, 847 (73 percent) were uncomplicated vaginal births (Ramin and Cunningham, 1995). Brachial plexus injuries, of varying severity, occurred in 4 of 737 infants weighing 4000 to 4500 g, and in 4 of 118 weighing more than 4500 g. Stated differently, 99.5 percent of fetuses weighing 4000 to 4500 g were delivered per vagina without injury, as were 96.6 percent of fetuses weighing more than 4500 g.

In the absence of clearly established benefits, which were documented in well-designed clinical trials, a recommendation of cesarean delivery based solely upon estimated fetal weight is not justified. Several of the recognized risk factors for macrosomia also constitute substantial increased risk factors for maternal operative morbidity and mortality. Consequently, maternal risks that accompany cesarean delivery must be considered critically in the development of management plans for the pregnancy with a suspected macrosomic fetus. For example, in the case of a 300-pound woman with poorly controlled diabetes and a fetus estimated to weigh in excess of 4000 g, cesarean delivery might reduce fetal risk. The risks for the woman described that accompany cesarean delivery may be sufficiently great, however, as to mitigate against the overall benefit to mother and child of this management approach. In several studies, there was an increased cesarean delivery rate but no improvement in neonatal outcome or reduction in birth injury among pregnancies in which labor was electively induced because of fetal macrosomia (Boyd and associates, 1983; Combs and colleagues, 1993; Delpapa and Mueller-Heubach, 1991).

Management of Shoulder Dystocia

 Management of Shoulder Dystocia.    The occurrence of fetal shoulder dystocia cannot be accurately predicted; therefore, the obstetrician must be expert in the management of this potentially devastating complication of childbirth. Reduction in the time interval from delivery of the head to delivery of the body is important to neonatal survival. An initial attempt to deliver the anterion shoulder with gentle traction, assisted by maternal expulsive efforts, is recommended by the American College of Obstetricians and Gynecologists (1991). Excessive traction on the fetal head or neck, or excessive rotation of the fetal body during delivery, however, may cause serious damage to the infant. A number of maneuvers have been described that can be used to relieve shoulder dystocia and effect delivery

 

MULTIFETAL PREGNANCY

1993 was the first year in American history when multiple births exceeded 100,000 (Ventura and colleagues, 1995). Specifically, there were more than 96,000 twin live births, and higher-order births included 3834 triplets, 277 quadruplets, and 57 quintuplets. As shown in Figure 38–1 , the introduction of ovulation-inducing agents in the late 1960s and assisted reproductive technologies in the 1970s has resulted in the number of multiple births rising faster than singletons (Luke, 1994). Jewell and Yip (1995) profiled women delivering plural births in the United States during the 1980s and observed that the increase in multiple births was due to use of fertility-stimulating therapy by older, typically white, women with high education status. As emphasized in Chapter 25 , the rise in multiple births is a consequence of changes in the demographics of American women and their pregnancies.

Powers and Kiely (1994) used United States linked birth/infant death certificates for 7.4 million singleton births and 156,690 twin births in 1985 and 1986 to measure the impact of twins on national infant morbidity and mortality. Although twins were relatively infrequent in the United States—approximately 1 in 94 pregnancies—they accounted for a disproportionately large share of adverse pregnancy outcomes, primarily as a consequence of preterm delivery. Similarly, at Parkland Hospital, twin infants represent only 1 in 44 births and yet account for 1 in 8 perinatal deaths (Table 38–1 ). Much of the perinatal mortality and morbidity attributable to multiple births is due to preterm delivery. In addition, fetuses in multiple gestations are vulnerable to a variety of unique complications such as twin-to-twin transfusion syndrome, so that stillbirth rates are also appreciably increased. Moreover, maternal complications such as pregnancy-induced hypertension and cesarean delivery are increased in multiple gestation (Table 38–1 ). As Powers and Kiely (1994) emphasized, postponing preterm delivery in twin pregnancy should become a national health priority because of the disproportionately large share of adverse pregnancy outcomes.

ETIOLOGY OF MULTIPLE FETUSES

Twin fetuses commonly result from fertilization of two separate ova, that is, double-ovum, dizygotic, or fraternal twins.  About one third as often twins arise from a single fertilized ovum that subsequently divides into two similar structures, each with the potential for developing into a separate individual, that is, single-ovum, monozygotic, or identical twins. Either or both processes may be involved in the formation of higher numbers of fetuses. Quadruplets, for example, may arise from one to four ova.

FRATERNAL VERSUS IDENTICAL TWINS

    Dizygotic twins are not in a strict sense true twins because they result from the maturation and fertilization of two ova during a single ovulatory cycle (Fig. 38–2 ). Newman (1923) wrote: “Strictly speaking, twainning is twinning or twoing—the division of an individual into two equivalent and more or less completely separate individuals.” Also, monozygotic or identical twins are not always identical. As discussed subsequently, the process of division of one fertilized zygote into two does not necessarily result in equal sharing of protoplasmic materials. In fact, dizygotic, or fraternal twins of the same sex, may appear more nearly identical at birth than do monozygotic twins; growth of monozygotic twin fetuses may be discordant and at times dramatically so.

GENESIS OF MONOZYGOTIC TWINS

Valid hypotheses to explain single-ovum, or monozygotic, twinning are lacking. Monozygotic twins arise from division of the fertilized ovum at various early stages of development as follows.

1.   If division occurs before the inner cell mass (morula) is formed and the outer layer of blastocyst is not yet committed to become chorion—that is, within the first 72 hours after fertilization—two embryos, two amnions, and two chorions will develop (Fig. 38–3 ). There will evolve a diamnionic, dichorionic, monozygotic twin pregnancy. The frequency of two chorions with monozygotic twinning in various reports has ranged from 18 to 36 percent (MacGillivray, 1978). There may be two distinct placentas or a single fused placenta (Fig. 38–4 ).

2.  If division occurs between the fourth and eighth day (Fig. 38–3 ), after the inner cell mass is formed and cells destined to become chorion have already differentiated but those of the amnion have not, two embryos will develop, each in separate amnionic sacs. The two amnionic sacs will eventually be covered by a common chorion, thus  giving rise to diamnionic, monochorionic, monozygotic twin pregnancy (Fig. 38–4C ).

3.  If, however, the amnion has already become established, which occurs about 8 days after fertilization, division will result in two embryos within a common amnionic sac, or a monoamnionic, monochorionic, monozygotic twin pregnancy.

4.  If division is initiated even later—that is, after the embryonic disk is formed—cleavage is incomplete and conjoined twins are formed.

Chimerism.     A chimera is an individual with a mixture of genotypes from more than one ovum and sperm. Possible mechanisms include double fertilization of one ovum and, in cases of nonidentical fetuses, the transfer of genetic material from one to the other across chorionic vascular anastomoses. For example, the transfer of primitive blood cells from one dizygotic twin fetus through a vascular anastomosis to the other twin can lead to the production in the recipient of two populations of blood cells of quite dissimilar blood types, or blood chimerism. The transposed cells are not destroyed, because exposure of the recipient twin to the dissimilar antigens of the donor twin early in fetal development renders the recipient twin tolerant to the donor tissues. Blood chimerism has been most commonly discovered at the time of blood typing when discordant blood types are found (Benirschke, 1974).

Chimerism, in which cell lines are derived from different zygotes, is to be distinguished from mosaicism, in which two or more cell lines of different chromosomal composition arise from the same zygote as the consequence of nondisjunction during meiotic division.

Superfetation and Superfecundation

 Superfetation and Superfecundation.    In superfetation, an interval as long as or longer than an ovulatory cycle intervenes between fertilizations. Superfetation has not been unequivocally demonstrated in women, although it is theoretically possible until the uterine cavity is obliterated by the fusion of the decidua capsularis to the decidua vera. Thus, superfetation requires ovulation during the course of an established pregnancy, as yet unproven in humans though known to occur in mares. Most authorities believe that the alleged cases of human superfetation result from marked inequality in growth and development of twin fetuses of the same gestational age, as described above.

 Superfecundation refers to the fertilization of two ova within a short period of time but not at the same coitus, nor necessarily by sperm from the same man. It may be that, in many cases, twin ova are not fertilized by sperm from the same ejaculate, but the fact can be demonstrated only in exceptional circumstances.

An instance of superfecundation, documented by Harris (1982), is demonstrated in Figure 38–5.  The mother was raped on the 10th day of her menstrual cycle and had intercourse 1 week later with her husband. She went into labor very near term and was delivered vaginally of a black infant whose blood type was A and a white infant whose blood type was O. The blood type of both the mother and her husband was O. HLA typing was not done. Terasaki and co-workers (1978) described the use of HLA typing to establish that dizygotic twins were sired by different fathers.

FREQUENCY OF TWINS

     The frequency of monozygotic twinning is relatively constant worldwide, at approximately one set per 250 births and is largely independent of race, heredity, age, and parity. The frequency was once thought to be independent of therapy for infertility; however, there is now evidence that the incidence of zygotic splitting is doubled following ovulation induction (Derom and colleagues, 1987). The incidence of dizygotic twinning is influenced remarkably by race, heredity, maternal age, parity, and especially, fertility drugs.

It is now apparent that the incidence of twin conceptions is much higher than indicated by figures based on the delivery of two fetuses. Kol and colleagues (1993) used transvaginal ultrasound to identify multiple gestational sacs at 5 to 6 weeks in 81 women, and then used serial ultrasound examinations to determine the natural history of twin gestations. Empty gestational sacs were identified in 21 women, most of whom (70 percent) subsequently delivered normal singletons.

Undoubtedly, some “threatened” abortions have resulted in actual abortion of one embryo from an unrecognized twin gestation while the other embryo continued its growth and development (Jauniaux and co-workers, 1988). Remarkably, fetal death as late as the end of the first trimester can be followed by complete fetal resorption, leaving no gross evidence at delivery that twins ever existed.

Multiple embryos and fetuses may develop in varying degrees ectopically—that is, outside the uterus. Such multiple ectopic pregnancies, as well as combined pregnancies in which there are one or more embryos or fetuses extrauterine as well as one or more intrauterine, are considered in Chapter 27.

Race

Race.    The frequency of multiple fetal births varies significantly among different races and ethnic groups (Table 38–2 ). Myrianthopoulos (1970) identified the  birth of twins in 1 of every 100 pregnancies among white women, compared with 1 of 80 pregnancies for black women. In some areas of Africa the frequency of twinning is very high. Knox and Morley (1960), in a survey of one rural community in Nigeria, found that twinning occurred once in every 20 births! Twinning in Asia is less common. In Japan, for example, among more than 10 million pregnancies analyzed, twinning was identified in only 1 of 155 births. These marked racial differences are the consequence of variations in the frequency of dizygotic twinning.

HEREDITY

    As a determinant of twinning, the genotype of the mother is much more important than that of the father. White and Wyshak (1964), in a study of 4000 records of the General Society of the Church of Jesus Christ of Latter-day Saints, found that women who themselves were a dizygotic twin gave birth to twins at the rate of 1 set per 58 births. Women not a twin, but whose husbands were a dizygotic twin, gave birth to twins at the rate of 1 set per 116 pregnancies. Bulmer (1960) reported that 1 out of 25 (4 percent) of twins’ mothers was also a twin but only 1 out of 60 (1.7 percent) of their fathers was a twin.

Maternal Age and Parity.    The positive effects of increasing maternal age and parity on the incidence of twinning were well demonstrated by Waterhouse (1950). For any increase in age up to about 40, or parity up to 7, the frequency of twinning increased. Twin pregnancies were less than one third as common in women under 20 with no previous children than in women 35 to 40 with 4 or more previous children. In Sweden, Pettersson and associates (1976) confirmed the remarkable increase in multiple birth rate associated with increased parity. In first pregnancies the frequency of multiple fetuses was 1.3 percent, compared with 2.7 percent in the fourth birth order.

In Nigeria, Azubuike (1982) identified the frequency of twinning to increase from 1 in 50 (2 percent) pregnancies among women pregnant for the first time to 1 in 15 (6.6 percent) for women pregnant six or more times!

Maternal Size.    Dizygotic twinning is more common in large and tall women than in small women (MacGillivray, 1986). This may be related more to nutrition than to body size alone. During World War II, when food deprivation was common, the incidence of dizygous twinning decreased in Europe. Even so, those women who had twins apparently did not consume more calories than those with singletons (Bulmer, 1959).

PITUITARY GONADOTROPIN

    Benirschke and Kim (1973) presented intriguing reasons for implicating elevated levels of endogenous follicle-stimulating hormone in the genesis of spontaneous dizygous twinning. A higher rate of dizygous twinning has been described for women who conceive within 1 month after stopping oral contraceptives, but not during subsequent months (Rothman, 1977). One possibility to account for the apparent increase is release of pituitary gonadotropin in amounts greater than usual during the first spontaneous cycle after stopping contraception. Another is increased fecundity among very recent users of oral contraceptives. Endogenous follicle-stimulating hormone levels may also be involved in the association of twinning with increased maternal age. The first sign of reproductive aging that has been consistently observed is an isolated rise in serum follicle-stimulating hormone (Klein and co-workers, 1996). This rise is temporally associated with the accelerated loss of primordial ovarian follicles that begins when a woman is about age 38.

INFERTILITY THERAPY

The induction of ovulation by use of gonadotropins (follicle-stimulating hormone plus chorionic gonadotropin) or of clomiphene remarkably enhances the likelihood of multiple ovulations. The incidence of multiple fetuses following gonadotropin therapy is 20 to 40 percent, and in one instance as many as 11 fetuses were aborted (Jewelewicz and Vande Wiele, 1975). Nonuplet pregnancy with spontaneous labor 27 weeks after ovulation induction with human pituitary gonadotropin has been described by Garrett and associates (1976). None of the nine infants survived.

With clomiphene therapy, the likelihood of multiple fetuses is somewhat less than with human menopausal gonadotropin. Even so, among nearly 2400 conceptions following clomiphene, 165 (7 percent) were known to be twin, 11 (0.5 percent) triplet, 7 (0.3 percent) quadruplet, and 3 (0.13 percent) quintuplet (Hoechst-Marion-Roussel, Kansas City, Missouri, 1972).

 Ovulation induction likely increases both dizygotic and monozygotic twinning. Derom and colleagues (1987) studied the incidence of monozygotic twinning in almost 1000 twin-pairs delivered in East Flanders, Belgium, and reported that the incidence of zygotic splitting was doubled after induced ovulation. Brambati and colleagues (1995) reported that multiple pregnancies resulting from ovarian stimulation are at higher risk of carrying at least one fetus affected by Mendelian or chromosomal anomalies, the incidence of which is directly related to the number of fetuses.

ASSISTED REPRODUCTION

ASSISTED REPRODUCTION.    The practice of attempting fertilization of all the ova collected after inducing superovulation, and then depositing in utero more than one blastocyst when available, accounts at least in part for the increased frequency of multifetal pregnancies that result from in vitro fertilization (Bradshaw and colleagues, 1992). McFaul and co-authors (1993) described their experiences with 148 women whose pregnancies resulted from in vitro fertilization (IVF) or gamete intrafallopian transfer (GIFT). Of these, 45 (30 percent) miscarried before 24 weeks and 35 of these were in the first trimester. Pregnancy losses included spontaneous abortions, blighted ova, missed abortions, and ectopic pregnancies. Of the 103 pregnancies that progressed beyond 24 weeks, 25 percent delivered preterm. Most of this excess pregnancy wastage was related to multiple gestations although increased obstetrical risks are also characteristic of singleton pregnancies resulting from assisted reproduction (Tanbo and colleagues, 1995). Goldfarb and colleagues (1996) estimated the combined costs of in vitro fertilization plus pregnancy care plus delivery was $39,249 for singletons or twins, and this increased to $342,788 for triplets or higher-order multiple gestations. Most of the costs for singleton or twins were attributed to in vitro fertilization, whereas most of the costs with triplets or more were due to neonatal intensive care. Gleicher and co-workers (1995) found that most couples considered the possibility of twins desirable, but higher-order multiple births were typically rejected because of the risks and costs.

SEX RATIOS WITH MULTIPLE FETUSES.

   The percentage of male conceptuses in the human species decreases as the number of fetuses per pregnancy increases. Strandskov and co-workers (1946) found the sex ratio, or percentage of males, for 31 million singleton births in the United States to be 51.6 percent. For twins it was 50.9 percent; for triplets, 49.5 percent; and for quadruplets, 46.5 percent. Two explanations have been offered. First, the differential fetal mortality between the sexes is well known, as it is for the newborn infant, child, and adult. Survival is always in favor of the female and against the male. The “population pressure” with multiple fetuses in utero may exaggerate the biological tendency noted in singleton pregnancies. A second explanation is that the female-producing zygote has a greater tendency to divide into twins, triplets, and quadruplets.

There are two important reasons to encourage determination of zygosity. First, inter-twin organ transplantation later in life can be facilitated by zygosity determinations at birth. Second, routine prenatal determination of chorionicity using ultrasound can be potentially beneficial in assessing obstetrical risks as well as guiding management of multiple gestations (Fisk and Bryan, 1993). Twin-specific complications in relation to zygosity are summarized in Table 38–3.  Clearly, monochorial twin gestations are at increased risk for a variety of pregnancy complications, some of which may be minimized by early antepartum diagnosis and treatment. Of particular importance are those monozygotic twins with shared circulation (twin-to-twin transfusion syndrome), shared amnionic sac (cord entanglement), and shared organs (conjoined twins).

Examination of Placenta.    A knowledgeably performed examination of the placenta and membranes serves to establish zygosity promptly in about two thirds of cases. The following system for examination is recommended. As the first infant is delivered, one clamp is placed on the portion of the cord coming from the placenta (Fig. 38–6 ). As the second infant is delivered, two clamps are placed on the cord. Three clamps are used to mark the cord of a third infant, and so on as necessary. Until the delivery of the last fetus is completed, it is important that each segment cord remain clamped to prevent hemorrhage through anastomosed vessels in the placenta.

Delivery of the placenta should be accomplished with care to preserve the attachment of the amnion and chorion to the placenta, because identification of the relationship of the membranes to each other is critical. With one common amnionic sac, or with juxtaposed amnions not separated by chorion arising between the fetuses, the infants are monozygotic. If adjacent amnions are separated by chorion, the fetuses may be monozygotic, but more often are dizygotic (Figs. 38–4 , 38–7 , and 38–8 ). If the infants are of the same sex, blood group studies to identify zygosity may be initiated at this time on samples of blood obtained from the umbilical cords. A difference in major blood groups is indicative of dizygosity. If these simple procedures fail to identify zygosity, more complicated techniques, such as DNA “fingerprinting,” can be used (Azuma and associates, 1989).

Infant Sex and Zygosity

 Infant Sex and Zygosity.    Although twins of opposite sex are almost always dizygotic, monozygotic twins may rarely be discordant for phenotypic sex. This occurs when one twin is phenotypically female due to Turner syndrome (45,X0) and its sibling is 46,XY. Pedersen and associates (1980) summarized the salient features of 16 cases of monozygotic twins in whom one or both twins had gonadal dysgenesis.

ULTRASOUND

Using high-resolution ultrasound equipment, it is possible to determine twins of different gender, separate placental sites, and dividing membrane relationships. Although information on zygosity can be obtained throughout pregnancy, ultrasonography in the first half is more accurate because the dividing amnionic membranes (Fig. 38–9 ) are more easily visualized when the fetuses are smaller (Stagiannis and colleagues, 1995).   Septal thickness of the dividing membranes less than 2 mm usually indicates monochorial twinning (Scardo and colleagues, 1995; Winn and associates, 1989). D’Alton and Dudley (1989), using magnified high-resolution ultrasound, were able to actually count the individual layers in the dividing membranes. Unfortunately, zygosity may not be ultimately determined in as many as 35 percent of twin sets without use of sophisticated genetic markers (Scardo and colleagues, 1995).

Fig. 4  Multifetal pregnancy in ultrasound

Fig. 5  Multifetal pregnancy in ultrasound

 

 

DIAGNOSIS OF MULTIPLE FETUSES

 Widespread use of prenatal ultrasound imaging has greatly decreased the incidence of overlooked twin gestations prior to delivery.

Fig. 6  Multifetal pregnancy

Ultrasound.    By careful ultrasonic examination, separate gestational sacs can be identified very early in twin pregnancy. Subsequently, the identification of each fetal head should be made in two perpendicular planes so as not to mistake a cross-section of the fetal trunk for a second fetal head. Sonographic scanning should detect practically all sets of twins. Indeed, one argument in favor of routine ultrasound screening is earlier detection of multiple fetuses (Chap. 46 ). LeFevre and co-workers (1993), in the Routine Antenatal Diagnostic Imaging and Ultrasound Study (RADIUS), randomized 7617 women to receive routine ultrasound scans at 18 to 20 weeks and again at 31 to 35 weeks. Outcomes of these pregnancies were compared with 7534 women randomized to ultrasound scanning only when clinically indicated. Virtually all multiple gestation (99 percent) were diagnosed before 26 weeks when routine ultrasound was used compared with 62 percent in women scanned only for specific indications. A total of 87 percent of multiple gestations were ultimately diagnosed before labor in these latter women. No perinatal benefits were identified as a result of routine ultrasound scanning to detect multiple gestations.

HISTORY AND CLINICAL EXAMINATION

History and Clinical Examination.    A familial history of twins by itself provides only a weak clue, but knowledge of recent administration of either clomiphene or pituitary gonadotropin provides a strong one.

Clinical examination with accurate measurement of fundal height, as described in Chapter 9 , is essential. During the second trimester, a discrepancy develops between gestational age determined from menstrual data and that from uterine size. The uterus that contains two or more fetuses becomes larger than one with a single fetus. Rouse and co-workers (1993) measured fundal heights in 336 well-dated twin pregnancies. Between 20 and 30 weeks, fundal heights were on average about 5 cm greater than expected for singletons of the same fetal age (Jimenez and co-workers, 1983).

In the case of a woman with a uterus that appears large for gestational age, the following possibilities are considered: (1) multiple fetuses, (2) elevation of the uterus by a distended bladder, (3) inaccurate menstrual history, (4) hydramnios, (5) hydatidiform mole, (6) uterine myomas, (7) a closely attached adnexal mass, and (8) fetal macrosomia late in pregnancy.

Other Diagnostic Aids.    A variety of techniques may be used to clinically suspect or diagnose multifetal gestation.

Fetal Parts.    Before the third trimester, it is difficult to diagnose twins by palpation of fetal parts. Even late in pregnancy it may be very difficult to identify twins by transabdominal palpation, especially if one twin overlies the other, if the woman is obese, or if hydramnios is present.

Fetal Heart Sounds

Fetal Heart Sounds.    Late in the first trimester, fetal heart action may be detected with generally available Doppler ultrasonic equipment (Chap. 2 ). Sometime thereafter it becomes possible to identify two fetal hearts if their rates are clearly distinct from each other as well as from that of the mother. It is possible by careful examination to identify fetal heart sounds in twins with the usual aural fetal stethoscopes at 18 to 20 weeks.

Radiological Examination

Radiological Examination.    A radiograph of the maternal abdomen to try to demonstrate multiple fetuses in the following circumstances will  provide no useful information and may be responsible for an incorrect diagnosis: (1) when taken before 18 weeks because the fetal skeletons are insufficiently radiopaque, (2) if the film is of poor quality from inappropriate exposure time or from malposition of the mother so that her upper abdomen and the fetus beneath are excluded from the x-ray, (3) when the mother is obese, (4) when there is hydramnios, and (5) if one fetus moves during the exposure. There are times, however, when the importance of diagnosing the presence of multiple fetuses surely overrides the minimal risk associated with a carefully obtained and interpreted radiograph.

BIOCHEMICAL TESTS

Biochemical Tests.    The amounts of chorionic gonadotropin in plasma and in urine, on average, are higher than those found with a singleton pregnancy, but not so high as to allow a definite diagnosis of multiple fetuses. Although not diagnostic of multiple gestation, the alphafetoprotein level in maternal plasma is commonly higher in pregnancies with twins  Currently, there is no biochemical test that in any individual case will reliably differentiate between the presence of one and more than one fetus.

MATERNAL ADAPTATION

In general, the degree of maternal physiological change is greater with multiple fetuses than with a single fetus. For example, the average increase in maternal blood volume induced during pregnancy with twin fetuses is significantly larger (Pritchard, 1965). Whereas the average increase in late pregnancy is about 40 to 50 percent with a single fetus, the  mean increase amounts to about 50 to 60 percent with twins. Measurements in the same woman late in one pregnancy with a single fetus and at the same time in another pregnancy with twins are indicative that, typically, maternal blood volume is about 500 mL greater with twins. Interestingly, the  average blood loss with vaginal delivery of 25 sets of twins averaged 935 mL, or nearly 500 mL more than with delivery of a single fetus. Both the remarkable increase in maternal blood volume and the increased iron and folate requirements imposed by a second fetus predisposed to a greater prevalence of maternal anemia.

Veille and associates (1985) used M-mode echocardiography to assess cardiac function in women with twin pregnancies. As expected, cardiac output was increased compared with singleton pregnancy, but end-diastolic ventricular dimensions were the same. During the third trimester,  cardiac output was increased as a result of both increased pulse rate and increased stroke volume. Stroke volume was higher by virtue of an increased shortening fraction, which suggests increased contractility.

The larger size of the uterus with multiple fetuses intensifies the anatomical changes that occur during pregnancy. The uterus and its contents may achieve a volume of 10 L or more and weigh in excess of 20 pounds! Especially with monozygotic twins, rapid accumulation of grossly excessive amounts of amnionic fluid—that is, acute hydramnios—may develop. In these circumstances it is easy to envision appreciable compression and displacement of many of the abdominal viscera as well as the lungs by the elevated diaphragm. The size and weight of the very large uterus may preclude more than a very sedentary existence for the woman.

In pregnancies with multiple fetuses further complicated by hydramnios, maternal renal function may become seriously impaired, most likely as the consequence of obstructive uropathy. Quigley and Cruikshank (1977) described two pregnancies with twin fetuses plus acute and severe hydramnios in which oliguria and azotemia developed. Maternal urine output and plasma creatinine levels promptly returned to normal after delivery. In the case of severe hydramnios, transabdominal amniocentesis may be employed to provide relief for the mother and, it is hoped, to allow the pregnancy to continue (see Chap. 29 , p. 662). Unfortunately, the hydramnios is often characterized by acute onset remote from term and by rapid reaccumulation following amniocentesis.

The various stresses of pregnancy and the likelihood of serious maternal complications will almost invariably be greater with multiple fetuses than with a singleton. This should be taken into account, especially when counseling the woman whose health is compromised and who is recognized early in pregnancy to have multiple fetuses. The same is true for a woman who is not pregnant but is considering treatment with agents used to induce ovulation.

PREGNANCY OUTCOME

Abortion.    Abortion is more likely with multiple fetuses. Detailed reviews of the pathology of spontaneous abortions have identified three times more twins among aborted pregnancy when compared with the ratios at term (Livingston and Poland, 1980; Uchida and co-authors, 1983). Monochorial twins greatly outnumber (18:1) dichorial twins, implicating monozygosity as a risk factor for spontaneous abortion. Anomalies and chromosomal errors, as in singletons, are also often found in twin abortuses. As described earlier, there is sonographic evidence that twins are frequently aborted subclinically or resorbed.

Malformations.    The incidence of congenital malformations is appreciably increased in twin and higher-order multiple gestations compared with singletons. The anomalies fall into one of two categories, malformations of the type that occur in single infants and those associated uniquely with multiple gestations. The latter include conjoined and acardiac twins, which are described later in this chapter.

Kohl and Casey (1975) identified  major malformations in approximately 2 percent of twin infants, compared with 1 percent of singletons. The frequency of minor malformations was approximately 4 percent in twins, compared with about 2.5 percent in singletons. Similar results were reported by Cameron and colleagues (1993). Baldwin (1991) has comprehensively reviewed these anomalies.

Rodis and associates (1990) reviewed chromosomal abnormalities in twin gestations and concluded that most evidence is suggestive of an increased incidence of aneuploidy. 

Persistent or chronic hydramnios is more likely to be associated with fetal anomalies of one or both twins. Hashimoto and colleagues (1986) subjectively identified increased amnionic fluid in one fourth of twin pregnancies. In half, hydramnios at midpregnancy was transient, and all of these fetuses were normal. In the 10 pregnancies in which hydramnios persisted, nine fetuses had anomalies.

BIRTHWEIGHT

 Birthweight.    Restricted fetal growth and preterm delivery are both important etiologies of the increased incidence of low birthweight in multifetal gestations (Buekens and Wilcox, 1993). In general, the larger the number of fetuses, the greater the degree of growth restriction. Moreover, when two or more fetuses are derived from a single ovum, the degree of growth restriction is likely to be greater than when each fetus is derived from a different ovum. The differences in birthweight were dramatic in the quintuplets shown in Figure 38–11.  When delivered at 31 weeks, the 3 infants from separate ova weighed 1420, 1530, and 1440 g, whereas the 2 derived from the same ovum weighed 990 and 860g. Although the birthweights of these 2 monozygotic infants were nearly the same, remarkable differences have been observed. Marked discordance in size may also complicate pregnancies in which each fetus arose from a separate ovum. For example, dizygotic twins, one of whom weighed 2300 and the other 785 g, were delivered at Parkland Hospital (Fig. 38–12 ). Both survived, but one remains appreciably smaller than the other.

Twin fetuses have been of particular interest to investigators seeking clues on the relative roles of “nature versus nurture” in human fetal growth. Excluding anomalies, fetal gender influences, and birthweight disparity due to placental insufficiency or vascular communications, restricted twin fetal growth appears to be primarily a result of diminished nurture during the third trimester. Figure 38–13  compares birthweights in more than 500,000 male singleton infants with more than 10,000 male twin infants. Twin birthweights closely parallel singletons until about 28 to 30 weeks, when twins begin to become progressively smaller than singletons. At approximately 34 to 35 weeks and thereafter, twin birthweights clearly diverge from singletons. Interestingly, it is also at this stage of gestation when the combined weight of twin fetuses reaches 4000 to 5000 g, the latter weight being quite rare in singletons—about 2 per 1000 births at Parkland Hospital in 1995 weighed more than 5000 g. Thus, the empirical upper fetal growth limit for singletons, and presumably upper limit of maternal support capacity, occurs at about 34 or 35 weeks in twin gestation. Luke and colleagues (1993) also described significant divergence of twin fetal growth at 35 weeks and beyond, and associated this diminished fetal growth with maternal weight gain less than 1 pound per week after 24 weeks. Lantz and associates (1996) found that low birthweight in twins occurred only in underweight women with poor weight gain during pregnancy. Moreover, twin growth restriction intensifies as the third trimester continues, such that at 38 weeks or later, the incidence of overt growth restriction quadruples to include almost half of twin births.

There is other circumstantial evidence that in utero crowding by multiple fetuses affects nurture presumably by overtaxing the capacity of the mother to provide nutrients. For example, Smith-Levitin and colleagues (1996) observed that selective reduction of triplets to twins before 12 weeks results in a growth pattern typical of twins rather than triplets who are growth restricted compared with twins. Thus, the number of fetuses residing in the uterus later in pregnancy, and not their embryonic potential, seems to govern growth. Another example that the maternal supply line is affected by the number of fetuses is provided by Casele and co-authors (1996) in their studies of maternal metabolic responses to eating and extended overnight fasting. Women with twins were more vulnerable to starvation ketosis after fasting compared with women with singleton pregnancies. This finding suggests that more maternal metabolic resources are funneled to twin fetuses. Yet another example that more than one fetus may overtax maternal support was provided by Maier and co-workers (1995). They measured umbilical venous erythropoietin concentrations in 100 twins and found that erythropoietin increased with advancing gestational age in twins but not in singletons. This finding was interpreted to suggest that placental perfusion and/or function decreases with advancing gestational age in twins.

DURATION OF GESTATION

 As the number of fetuses increases, the duration of gestation decreases . Approximately 50 percent of twins deliver at 36 weeks or less and half of triplets or higher-order multiple gestations are delivered before 32 weeks. Indeed, preterm delivery before 37 weeks occurs in almost all higher-order multiple gestations.  The average gestational age at delivery of twins is approximately 36 weeks (Santema and colleagues, 1995a). Similarly, the mean gestational age at delivery in 40 triplet pregnancies was 32 to 33 weeks (Albrecht and Tomich, 1996; Santema and colleagues, 1995a) compared with 31 weeks in 37 quadruplet pregnancies (Barton and colleagues, 1996).

PREMATURITY

 .    Preterm delivery is the major reason for the increased risk of neonatal death and morbidity in twins. Gardner and colleagues (1995) compared outcomes of  preterm twin infants with preterm singletons delivered at the same gestational ages to determine if twins had an intrinsic increased risk of morbidity due to prematurity. Preterm twins did not have significantly more respiratory distress syndrome, intraventricular hemorrhage, or necrotizing enterocolitis than similar gestational-age singletons. Long-term major handicaps associated with prematurity were also not increased in twins compared with same gestational-age singletons. Thus, the primary neonatal problem with twin gestation is not increased vulnerability to the morbidity of prematurity, but simply more frequent preterm delivery. Similar findings were reported by Kilpatrick and colleagues (1996).

Gardner and associates (1995) also found that the causes of preterm birth differed between twins and singletons. Spontaneous preterm labor accounted for a larger proportion of twins delivered before 37 weeks compared with singletons whereas the reverse was true for preterm ruptured membranes. Indicated preterm delivery accounted for equal proportions of prematurely delivered twins and singletons. Maternal hypertension, fetal growth restriction, and placental abruption were the main indications for preterm delivery of twins.

PROLONGED PREGNANCY

    Is there an upper safe limit of twin gestation? Almost 30 years ago Dunn (1969) suggested that a twin pregnancy of 40 weeks or more should be considered postterm. This was based on the observation that twin stillborn infants delivered at 40 weeks or beyond had features similar to postmature singletons (see Chap. 35 , p. 829). More recently, Kiely (1990) reported that twins born at 40 weeks or more were actually lighter than those born at 38 to 39 weeks, suggesting that intrauterine growth for twins stops after 39 weeks. Similarly, Luke and colleagues (1993) as well as Minakami and Sato (1996) concluded that twins were “postterm” after 38 weeks because the incidence of fetal growth restriction and associated morbidity increased significantly in twins delivered between 39 and 41 weeks compared with delivery at 38 weeks or less. At Parkland Hospital, twin gestations have empirically been considered for many years to be prolonged at about 40 weeks gestation.

SUBSEQUENT DEVELOPMENT

    In Norway, Nilsen and associates (1984) evaluated the physical and intellectual development of male twins at 18 years of age. Compared with singletons, twice as many twins were found to be physically unfit for military service. They attributed this to preterm delivery rather than twinning. General intelligence did not appear to differ.

The pattern of subsequent development of the growth-retarded infant from a multifetal pregnancy varies. Babson and Phillips (1973), for example, reported that in monozygotic twins whose birthweights differed on the average by 35 percent, the twin who was smaller at birth remained so into adulthood. Height, weight, head circumference, and intelligence often remained superior in the twin who weighed more at birth. Fujikura and Froelich (1974), however, failed to confirm a significant difference in mental and motor scores.

Baigts and co-workers (1982) studied 17-year-old monozygotic twins who had body frames that were quite similar but who were remarkably dissimilar in weight, as they were at birth. The investigators documented hyperplasia of adipocytes in the heavier twin compared with her lighter sister. They suggested that intrauterine nutritional status helps to determine adipocyte numbers and the way the body evolves. Others have concluded that genetic heritage in twins is more important than environment in determining body mass (Bouchard and co-workers, 1990; Stunkard and co-workers, 1990).

UNIQUE COMPLICATONS

 There are a number of unique complications that occur in multiple fetuses simply because they are multiples. These unique complications have been best described in twins, although they also occur in higher-order multiple gestations.

MONOAMNIONIC TWINS

    There is an extremely high fetal death rate with the relatively rare variety of  monozygous twinning in which both fetuses occupy the same amnionic sac—that is, monoamnionic twins. A common cause of death is intertwining of their umbilical cords, which has been estimated to complicate 50 percent or more of cases (Benirschke, personal communication, 1983). An example is provided in Figure 38–15.  Approximately 1 percent of monozygotic twins are mono-amnionic. Unexplained rupture of the dividing membrane has been described and is associated with all the morbidity and mortality of true monoamnionic twins (Gilbert and colleagues, 1991). We have observed a case of monoamnionic twins in which at 31 weeks one twin was confirmed to be dead while the other appeared to be thriving. Four weeks later, after spontaneous labor, an apparently healthy infant was delivered. The other fetus was badly decomposed and weighed 770 g. The two umbilical cords were in close proximity at their insertions into the single placenta. The cords were entwined for nine complete turns!

Once diagnosed, management of monoamnionic twins is somewhat problematic due to the unpredictability of fetal death due to cord entanglement. Belfort and colleagues (1993) and Aisenbrey and co-workers (1995) used color-flow Doppler ultrasonography to diagnose umbilical cord entanglement. Antepartum fetal heart rate monitoring was used successfully tocontinue pregnancy or, alternatively, decide when delivery for cord compression decelerations was indicated. Carr and co-authors (1990) reviewed 24 sets of monoamnionic twins where all the fetuses were known to be alive before 18 weeks. At 30 weeks, 70 percent of the fetuses were alive and there were no additional deaths prior to delivery at an average of 36 weeks. They concluded that the risks of early delivery to prevent cord accidents outweighed the risks of fetal death as a result of monoamnionic status alone. Similar experiences were reported by Tessen and Zlatnik (1991), in their description of 20 monoamnionic twin pregnancies at the University of Iowa Hospital between 1961 and 1989. There were no fetal deaths after 32 weeks, suggesting that prophylactic preterm delivery may not be indicated in all cases.

CONJOINED TWINS

    In the United States, united or conjoined twins are commonly referred to as Siamese twins, after Chang and Eng Bunker of Siam (Thailand), who were displayed worldwide by P.T. Barnum. If twinning is initiated after the embryonic disc and the rudimentary amnionic sac have been formed, and if division of the embryonic disc is incomplete, conjoined twins result (see Fig. 38–3 ). When each of the joined twins is nearly complete, the commonly shared body site may be (1) anterior (thoracopagus), (2) posterior (pyopagus), (3) cephalic (craniopagus), or (4) caudal (ischiopagus).  The majority are of the thoracopagus variety (Figs. 38–16  and 38–17 ). As reviewed by van den Brand and associates (1994), the diagnosis of conjoined twins can frequently be made at midpregnancy using sonography (Fig. 38–17 ).

When the bodies are duplicated only partly, the attachment more often is lateral. The incomplete division of the embryonic disc may begin at either or both poles and produce two heads; two, three, or four arms; two, three, or four legs; or some combination thereof. The frequency of conjoined twins is not well established. At Kandang Kerbau Hospital in Singapore, Tan and co-workers (1971) identified seven cases of conjoined twins among somewhat more than 400,000 deliveries (1 in 60,000).

Vaginal delivery of conjoined twins is possible because the union is most often somewhat pliable, although dystocia is common. If the fetuses are mature, vaginal delivery may be traumatic. Surgical separation of conjoined twins may be successful when organs essential for life are not shared (Fig. 38–16 ).

ACARDIAC TWIN

Twin reversed-arterial-perfusion (TRAP) sequence is a rare (1 in 35,000 births), but serious complication of monozygotic multiple gestation. It has been hypothesized that hemodynamically significant vascular placenta anastomoses during embryogenesis result in inadequate perfusion of one twin leading to invariably lethal anomalies that include acardia and acephalus (van Allen and colleagues, 1983). An example of an acardiac twin is shown in Figure 38–18.  It demonstrates acephalus as well as complete malformation of the upper torso. One twin serves to pump blood retrograde (pump twin) to its sibling (recipient twin). Typically the pump twin is structurally normal, but it is at risk for in utero heart failure. Without treatment the pump twin dies in 50 to 75 percent of cases. Moore and colleagues (1990) have described the outcome of 49 pregnancies complicated by acardiac twinning.

Quintero and colleagues (1994) have reviewed methods of in utero treatment of acardiac twinning where the goal is interruption of the vascular communication between the pump and recipient twins. They also have described successful use of transabdominal fetoscopy to ligate the umbilical cord of 11 acardiac twins at approximately 21 weeks (Quintero and co-authors, 1996).

VASCULAR COMMUNICATIONS BETWEEN FETUSES

    With rare exceptions, vascular communications between twins are present only in monochorial placentas (Baldwin, 1991; Robertson and Neer, 1983). Nearly 100 percent of such placentas have vascular anastomoses, but there is marked variation in the number, size, and direction of these seemingly haphazardly formed connections. Artery-to-artery anastomoses on the chorionic surface of the placenta (Fig. 38–19 ) are the commonest pattern and have been identified in up to 75 percent of monochorial placentas. Vein-to-vein and artery-to-vein are each found in approximately 50 percent of similar placentas. One vessel may have several connections, sometimes to both arteries and veins. In contrast to these vascular connections on the surface of the chorion, there are artery-to-vein communications through the intervening capillary bed of the villous tissue of the placenta. These deep arteriovenous anastomoses create a “common villous district” or “third circulation” that has been identified in approximately half of monochorial placentas (Fig. 38–20 ).

These vascular communications can potentially cause hemodynamically significant shunts between fetuses. Most potential shunt situations, however, are hemodynamically balanced and of little fetal consequence. There are two patterns of hemodynamically significant anastomotic circulations: acardiac twining (see preceding description) and the twin-to-twin transfusion syndrome. The incidence of the latter syndrome is unclear, but up to approximately one fourth of monochorial twins have clinical features of this syndrome (Galea and co-workers, 1982).

DEATH OF ONE FETUS

.    On occasion, one fetus succumbs remote from term, but the pregnancy continues with one living fetus. At delivery, the dead fetus with placenta and membranes may be identified readily but may be compressed appreciably (fetus compressus) or may be flattened remarkably through loss of fluid and most of the soft tissue (fetus papyraceous). The papyraceous fetus shown in Figure 38–23  died at midpregnancy while the other fetus and placenta thrived. The dead fetus shown in Figure 38–24  has become almost a shadow of itself compressed onto its placenta, which was separate from the placenta of the surviving twin.

Theoretically, at least, acquired coagulation defects—disseminated intravascular coagulation, consumptive coagulopathy—could be triggered in the mother by the death of one of multiple fetuses. In these cases, dangerous maternal hypofibrinogenemia and troublesome hemorrhage at delivery may develop when both of twin fetuses are dead in utero for a prolonged period (Chap. 33 ). We have observed transient, spontaneously corrected consumptive coagulopathy when one fetus died and was retained in utero along with the other who was alive (see Fig. 33–3 ). As concern mounted over the well-being of the mothers and their surviving fetuses, the fibrinogen concentration rose spontaneously and the level of serum fibrinogen–fibrin degradation products fell to normal. At delivery the portions of the placenta that supplied the living fetus appeared quite normal, whereas the part that had once provided for the dead fetus was the site of massive fibrin deposition. This may have accounted directly for the fall in maternal fibrinogen and in turn an increase in fibrin degradation products, or it may have served to block the escape of thromboplastin from fetus and placenta into the maternal circulation and thereby prevented disseminated intravascular coagulation. Both mechanisms may also have been operational until extensive fibrosis was achieved. The fetuses who were alive at the time of demise of the womb-mate continued to thrive in utero as they did after birth. At birth, their plasma fibrinogen levels, serum fibrinogen–fibrin degradation products, and platelet counts were normal.

Romero and co-workers (1984) observed maternal hypofibrinogenemia to develop sometimes after death of one of twin fetuses. The hypofibrinogenemia was corrected in the mother by heparin infusion. The first time heparin therapy was discontinued the hypofibrinogenemia recurred, but the next time heparin was stopped hypofibrinogenemia did not recur. Presumably, by the second time, consumption coagulopathy in the mother was arrested by sealing off the maternal vascular bed with fibrin. The live-born infant appeared normal at 14 months of age.

The risk to a surviving fetus of developing serious consumptive coagulopathy may theoretically be enhanced if there are anastomoses between the fetal circulations, commonly found with monochorionic twins. So far, however, we have not identified consumptive coagulopathy in cord blood of the living monozygotic twin when the other had been long dead. Benirschke (1993) has concluded that it is implausible that degenerating material from a dead fetus could be transported back to a living sibling.

Santema and co-workers (1995b) assessed the cause and outcome of 29 consecutive twin pregnancies where one of the fetuses died after 20 weeks. The incidence of such single twin fetal death was 5 percent in 531 twin gestations. There were no cases of fetal brain damage and no cases of maternal or fetal coagulopathy. The causes of fetal death were not clear in all cases; associations included monochorionic placentation and severe preeclampsia. These investigators concluded that the  risks of preterm delivery exceed the low risks related to continuation of multiple pregnancy after diagnosis of fetal death, and we agree with their recommendations of conservative management of the living fetus(es).

Impending Death of One Fetus

 Impending Death of One Fetus.    In a 15-year period at Parkland Hospital, during which time more than 2000 twin gestations have been delivered, four pregnancies were encountered where antepartum fetal death was judged imminent. Abnormal antepartum tests of fetal health in one twin fetus but not the other pose a particular dilemma because delivery may be the best option for the compromised fetus, yet may result in death due to immaturity in the unaffected twin (Fig. 38–25 ). When fetal lung maturity is confirmed, salvage of both the healthy fetus and its jeopardized sibling is possible. Unfortunately, ideal management when the healthy fetus is very immature is problematic.

COMPLETE HYDATIDIFORM MOLE AND COEXISTING FETUS

Complete Hydatidiform Mole and Coexisting Fetus.    This entity is different from a partial molar pregnancy because there are two separate conceptuses, with a normal placenta in one twin and a complete molar gestation in the other. The distinction between partial and complete mole (see Chap. 30 , p. 677) has important clinical implications, because persistent trophoblastic tumor occurs more commonly following complete hydatidiform mole (Berkowitz and Goldstein, 1992). Indeed, Steller and co-workers (1994) reported that 5 of8 women with complete molar twinning required chemotherapy for persistent gestational trophoblastic tumor and three of these had metastases. The optimal management of complete hydatidiform mole with coexisting fetus is uncertain, especially when the pregnancy is desired.

ANTEPARTUM MANAGEMENT OF TWIN PREGNANCY

 To reduce perinatal mortality and morbidity in pregnancies complicated by twins, it is imperative that (1) delivery of markedly preterm infants be prevented, (2) failure of one or both fetuses to thrive be identified and fetuses so afflicted be delivered before they become moribund, (3) fetal trauma during labor and delivery be eliminated, and (4) expert neonatal care be provided.

Diet

Diet.    The requirements for calories, protein, minerals, vitamins, and essential fatty acids are further increased in women with multiple fetuses. The Recommended Dietary Allowances made by the Food and Nutrition Board of the National Research Council for uncomplicated pregnancy should not only be met but in most instances exceeded (Chap. 9 ). Consumption of energy sources should be increased by another 300 kcal/day. Iron supplementation of 60 to 100 mg/day is recommended.  Folic acid, 1 mg/day, is given, although a diet adequate in protein provided from a variety of sources should supply adequate amounts of folate. Sodium restriction is not beneficial.

Maternal Hypertension.    Pregnancy-induced and -aggravated hypertension are much more likely to develop in pregnancies with multiple fetuses. Skupski and colleagues (1996) observed that the rate of preeclampsia is increased in triplets when compared with triplets reduced to twins. This suggests that fetal number and placental mass are involved in the pathogenesis of preeclampsia (Chap. 31 ). Interestingly, Hardardottir and colleagues (1996) have reported that women with preeclampsia due to high-order multifetal gestations more often develop epigastric pain, hemolysis, and thrombocytopenia as a result of their disease.

Hypertension not only develops more often but also tends to develop earlier and to be more severe. In their analysis of 3407 twin pregnancies compared with 8287 singletons in Washington state, Coonrad and associates (1995) reported that twin pregnancy carries nearly a fourfold increased risk in preeclampsia, independent of race and parity, and the risk in a nulliparous woman is 14 times that of a singleton. As shown in Table 38–1 , the incidence of pregnancy hypertension in women with twins is 16 percent at Parkland Hospital.

Antepartum Surveillance

Antepartum Surveillance.    As discussed earlier, fetal growth is slower in multiple pregnancies than in singleton gestations, and it also may be unequal within a twin pair. For these reasons serial sonography is usually employed throughout the third trimester. Abdominal circumference differences of 20 mm or more are usually, but not always, predictive of intrapair birthweight differences exceeding 20 percent (Hill and associates, 1994). It is probable, however, that the likelihood of significant discordancy increases as additional fetal dimensions within a pair demonstrate inequality. Associated oligohydramnios may be particularly meaningful.

Magann and colleagues (1995b), using dyedilution technique, measured both amnionic fluid volumes in 47 uncomplicated diamnionic twin gestations between 27 to 38 weeks. The average amnionic fluid volume per twin sac was 877 mL, which is similar to that reported for singletons. The normal range of amnionic fluid volume for one fetus was 215 to 2500 mL. These results suggest, that in the aggregate, a diamnionic twin gestation has twice the amnionic fluid volume of a singleton. Magann and co-workers (1995a) also reported that oligohydramnios (less than 500 mL) is poorly identified by any sonographic method in twin gestations. Porter and associates (1996) have provided normal values for the amnionic fluid index for twin pregnancies.

Tests of Fetal Health

Tests of Fetal Health.    Gallagher and colleagues (1992) analyzed fetal heart rate accelerations, fetal movement, and other behavioral states in 15 twin pairs. If one twin of a pair was awake or asleep so was its sibling; however, accelerations and movements were usually not coincidental. An example of such asynchrony of accelerations is shown in Figure 38–26.

As described in Chapter 43 , there are several methods of assessing fetal health in singleton pregnancies. Similarly, use of the nonstress test or biophysical profile is common in contemporary management of twin or higher-order multiple gestations. The complexity of complications associated with multiple gestations as well as the potential technical difficulties in separating fetuses during antepartum testing appears to limit the usefulness of these methods in multiple gestations. For example, Saacks and co-workers (1995) observed that  the antepartum death rate of twin fetuses did not change between 1952 to 1962 and 1983 to 1993 despite the availability of fetal testing during the latter decade.

.PREVENTION OF PRETERM DELIVERY

    Several techniques have been applied in attempts to prolong multifetal gestations. These include bed rest, especially through hospitalization, prophylactic administration of b-mimetic drugs, and prophylactic cervical cerclage.

Bed Rest

Bed Rest.    Most recent evidence suggests that routine hospitalization is not beneficial (Goldenberg and colleagues, 1994). For example, Crowther and co-workers (1990) randomized hospitalization in 139 Zimbabwe women with twin pregnancies and found that hospitalization did not prolong pregnancy or improve infant survival, although bed rest incumbent with hospitalization did improve fetal growth. At Parkland Hospital, elective hospitalization at 26 weeks was compared longitudinally with outpatient management and no advantages were found for routine hospitalization (Andrews and colleagues, 1991). Importantly, almost half of the twin pregnancies studied at Parkland Hospital required admission for specific indications such as hypertension or threatened preterm delivery. Currently at our hospital women with twins are managed as outpatients with frequent prenatal visits and prompt hospitalization for complications.

 Special prenatal clinic sessions, limited physical activity, early work leave, and structured maternal education on the risks of preterm delivery have been advocated to be effective in reducing preterm births in women with twin pregnancies (Ellings and colleagues, 1993; Taffoxeau and associates, 1995).

Beta-mimetics and Other Tocolytic Drugs

Beta-mimetics and Other Tocolytic Drugs.    Most randomized trials of b-mimetics in twin pregnancies have not shown significant reductions in preterm delivery rates. Ashworth and associates (1990) were unable to substantiate any benefits for prophylactic b-mimetic therapy with salbutamol in twin gestations. As described in Chapter 34 , there are very few randomized studies of other tocolytic drugs compared with untreated controls and few specifically focus on multiple gestation.

CORTICOSTEROIDS FOR FETAL MATURATION

.    Although acknowledging that there is no satisfactory evidence that corticosteroids benefit multiple fetuses, the Consensus Development Conference on Corticosteroids for Fetal Maturation (1994) sponsored by the National Institutes of Health essentially recommended treatment for women with multiple gestations and impending delivery.

CERCLAGE

    No significant reduction in preterm delivery or perinatal deaths has been demonstrated from prophylactic cervical cerclage (Dor and associates, 1982; Grant, 1991).

PULMONARY MATURATION

    Pulmonary maturation, measured by determination of the lecithin–sphingomyelin ratio, is usually synchronous in twins (Leveno and associates, 1984). Moreover, although this ratio usually exceeds 2 by 36 weeks in singleton pregnancies, it often does so by about 32 weeks in multifetal pregnancy. In some cases, however, there may be marked disparity of pulmonary function. We observed the lecithin– sphingomyelin ratio with quintuplets to vary from less than 2 for the largest infant, who weighed 1530 g at 32 weeks and was of appropriate size for his gestational age, to greater than 5 for the severely growth-restricted smallest infant, who weighed 860 g. The largest infant developed appreciable respiratory distress, whereas the smallest infant did not.

Expectant Management of Ruptured Membranes

Expectant Management of Ruptured Membranes.    Twin gestations with preterm ruptured membranes are managed expectantly much like singleton pregnancies (Chap. 34 ). Mercer and colleagues (1993) compared outcomes of twin and singleton pregnancies with preterm membrane rupture (at 19 to 36 weeks) and found that labor ensued earlier in twins. Specifically, the median time from membrane rupture to delivery was 1.1 days in twins compared with 1.7 days in singletons. Virtually all twins and singletons (greater than 90 percent) delivered within 7 days of ruptured membranes.

Delayed Delivery of Second Twin

Delayed Delivery of Second Twin.    In the circumstances where one of the fetuses has been expelled very preterm and uterine activity then ceased, the pregnancy has occasionallly been allowed to continue with delivery of another fetus days to even many weeks later. Cardwell and associates (1988) described delivery of triplets at 24, 241¤2, and 26 weeks. Wittman and colleagues (1992) reviewed delayed delivery and reported an additional four cases with intervals ranging between 41 and 143 days. Arias (1994) used cervical cerclage, tocolysis, and antibiotics after vaginal delivery of one fetus between 15 and 23 weeks in six women with twins and two others with triplets. Of the 18 total fetuses involved in this study, 12 died and four others sustained severe morbidity. Only two infants lived without significant morbidity. One of these was delivered at 35 weeks after its sibling had delivered at 18 weeks. The other healthy survivor was delivered at 38 weeks and its sibling had been delivered at 22 weeks.

DELIVERY OF TWIN FETUSES

Labor.    Many complications of labor and delivery, including preterm labor, uterine dysfunction, abnormal presentations, prolapse of the umbilical cord, premature separation of the placenta, and immediate postpartum hemorrhage, are encountered much more often with multiple fetuses. For these reasons, certain precautions and special arrangements are prudent when delivery of two or more fetuses is expected. Recommendations for intrapartum management follow.

1.  An appropriately trained obstetrical attendant should remain with the mother throughout labor. Continuous external electronic monitoring or, if the membranes are ruptured and the cervix dilated, evaluation of both fetuses by simultaneous internal and external electronic monitoring, is typically employed.

2.  Blood transfusion products should be readily available.

3.  An intravenous infusion system capable of delivering fluid rapidly should be established. In the absence of hemorrhage or metabolic disturbance during labor, lactated Ringers with aqueous dextrose solution is infused at a rate of 60 to 120 mL/hr.

4.  Ampicillin, 2 g intravenously, is administered every 6 hours for prevention of group B Streptococcus neonatal infection when preterm labor is diagnosed.

5.  An obstetrician skilled in intrauterine identification of fetal parts and intrauterine manipulation of the fetus should be present.

6.  An experienced anesthesiologist should be immediately available in the event that intrauterine manipulation or cesarean delivery is necessary.

7.  For each fetus, two people, one of whom is skilled in resuscitation and care of newborns, are appropriately informed of the case and remain immediately available.

8.  The delivery area should provide adequate space for all members of the team to work effectively. Moreover, the site should be appropriately equipped to take care of all possible maternal problems plus resuscitation and maintenance of each infant.

Presentation and Position

Presentation and Position.    With twins, all possible combinations of fetal positions may be encountered. Either or both fetuses may present by the cephalic, breech or shoulder. As shown in Figure 38–27 ,  the most common presentations at admission for delivery are cephalic-cephalic, cephalic-breech, and cephalic-transverse. Importantly, these presentations, especially those other than cephalic-cephalic, are unstable before and during labor or delivery. Compound, face, brow, and footling breech presentations are relatively common, especially when the fetuses are quite small, there is excess amnionic fluid, or maternal parity is high. Prolapse of the cord is fairly common in these circumstances.

The presentation can often be ascertained by real-time sonography. If any confusion about the relationship of the twins to each other or to the maternal pelvis persists, a single anteroposterior x-ray of the abdomen may be helpful.

Induction or Stimulation of Labor

 Induction or Stimulation of Labor.    Labor is generally shorter with twins, but rupture of the membranes without effective labor, and prolonged inefficient labor with or without previous rupture of the membranes, do develop. These problems are often handled better by cesarean delivery unless there is little hope of salvaging the infants because of their gross immaturity. Termination of pregnancy is occasionally desirable before the spontaneous onset of labor, as with severe pregnancy-induced hypertension. In these circumstances, if the presenting part is well fixed in the pelvis and the cervix dilated somewhat, amniotomy will often initiate labor and effect delivery. There is no reluctance by some obstetricians to give oxytocin by dilute intravenous infusion to initiate or to stimulate labor in pregnancies complicated by multiple fetuses. Satin and co-workers (1996) compared outcomes in 55 women with twins and given oxytocin for augmentation or induction for labor to 55 matched singleton pregnancies. Women with twin pregnancies responded similarly as singletons.

Analgesia and Anesthesia

Analgesia and Anesthesia.    During labor and delivery of multiple fetuses, deciding what to use for analgesia and for anesthesia is unusually difficult because of the frequency of and problems imposed by (1) prematurity, (2) maternal hypertension, (3) desultory labor, (4) need for intrauterine manipulation, and (5) uterine atony and hemorrhage after delivery. Continuous epidural or caudal analgesia in hypertensive women, or those who have hemorrhaged, may cause hypotension with inadequate perfusion of vital organs, especially the placenta. The woman pregnant with multiple fetuses is even more vulnerable to supine hypotension during labor and delivery. Moreover, conduction analgesia may cause or further aggravate prolonged labor and will not provide adequate uterine relaxation for intrauterine manipulation when such is necessary.

Crawford (1987) described 105 women with twins delivered vaginally who were given epidural analgesia. Epidural analgesia prolonged the interval from complete dilatation until delivery by approximately 60 minutes. Interestingly, the mean delivery intervals between delivery of the first and second twins were not altered by epidural analgesia.

Either balanced general anesthesia or conduction analgesia, administered epidurally or in the subarachnoid space, has proved satisfactory at Parkland Hospital for cesarean delivery of twins. Pudendal block skillfully administered along with nitrous oxide plus oxygen provides appreciable relief of pain for spontaneous delivery. When intrauterine manipulation is necessary, as with internal podalic version, uterine relaxation is probably best accomplished with isoflurane. Although these agents provide effective relaxation for intrauterine manipulation, they also cause an increase in blood loss during the third stage until these drugs wear off and the uterus regains its ability to contract (Chap. 15 ).

Interval Between First and Second Twins

Interval Between First and Second Twins.    In the past, the interval between delivery of the first and second twins was commonly cited to be safest if less than 30 minutes. Subsequently, as shown by Rayburn and colleagues (1984) as well as others, if continuous fetal monitoring is employed, there is a good outcome even if this interval is longer. Of 115 twin-pairs at 34 weeks or more, the mean interval between delivery of twins was 21 minutes, but it ranged from 1 to 134 minutes. In 60 percent, the interval was 15 minutes or less. Importantly, there was no excess trauma or evidence for fetal depression in those born after the 15-minute interval. As expected, the cesarean delivery rate was much higher if the interval was more than 15 minutes (18 percent) than if the interval was less than 15 minutes (3 percent). Saacks and co-workers (1995) found that the time interval between delivery of twin A and twin B increased significantly between 1952 and 1993. The median interval was 11 minutes in the most recent years they studied, however, probably indicating that the spontaneous delivery interval between twins is typically quite brief.

Vaginal Delivery

Vaginal Delivery.    The presenting twin typically bears the major brunt of dilating the cervix and the remaining soft tissues of the birth canal. Seldom with cephalic presentations are there unusual problems with delivery of the first infant. After appropriate episiotomy, spontaneous delivery or delivery assisted by the use of outlet forceps usually proves satisfactory. When the first fetus presents as a breech, however, major problems are most likely to develop if (1) the fetus is unusually large and the aftercoming head taxes the capacity of the birth canal, (2) the fetus is quite small so that the extremities and trunk are delivered through a cervix inadequately effaced and dilated for the head to escape easily, or (3) the umbilical cord prolapses. When these problems are anticipated or identified, cesarean delivery will often be the better way to effect delivery, except in those instances in which the fetuses are so immature that they will not survive. Otherwise, breech delivery may be accomplished as described in Chapter 21.

 The phenomenon of locked twins is rare, and according to Cohen and co-workers (1965) occurred only once in 817 twin gestations. For locking to occur, the first fetus must present by the breech and the second by the cephalic. With descent of the breech through the birth canal, the chin of the first fetus locks in the neck and chin of the second cephalic fetus. Cesarean delivery is recommended when the potential for locking is identified.

Most obstetricians plan vaginal delivery for cephalic-cephalic presenting twins if satisfactory labor has been established. The optimal delivery route for cephalic-noncephalic presenting twins is controversial, particularly when prematurity is a concern (American College of Obstetricians and Gynecologists, 1989). Many of the issues involved in vaginal delivery of breech second twins are similar to those for singletons (Chap. 18 ), with the added concern that second-born twins have historically fared worse than their first-born siblings. As a result, cesarean delivery is commonly used to deliver other than cephalic-cephalic presenting twins, and this likely accounts for the high cesarean rate in twins. For example, Saacks and associates (1995) chronicled twin management at the University of North Carolina Hospitals between 1952 and 1993, and found that abdominal delivery of both infants was used in 41 percent of pregnancies managed between 1983 and 1993. Importantly, cesarean delivery was performed for the second infant after vaginal birth of the presenting fetus in another 8 percent of twin gestations. As shown in Table 38–1 , approximately 50 percent of twin pregnancies are delivered by cesarean at Parkland Hospital.

There are several reports attesting to the safety of vaginal delivery of the second noncephalic twins larger than 1500 g (Blickstein, 1987; Chervenak, 1985; Gocke, 1989; and their associates) as well as those weighing less than 1500 g (Davidson and co-workers, 1992; Rydhstrom, 1990). Fishman and colleagues (1993) reported their experiences with vaginal delivery of breech second twins at Los Angeles County Hospital between 1985 and 1988. A total of 781 twin pregnancies were delivered during this time period, and overall 48 percent of the women were delivered abdominally. About 50 percent of second twins delivered vaginally were cephalic. Another 183 breech infants were delivered vaginally and 95 percent of these were by total extraction. There were no significant differences in perinatal outcomes in births greater than 1500 g when vaginal breech extractions were compared with cephalic births of second twins. These authors did not specify how women were selected for vaginal breech delivery of second twins. Unfortunately, and as emphasized by Chauhan and colleagues (1995), there are no large randomized trials to help resolve the uncertainty about vaginal or cesarean delivery for noncephalic second twins.

Vaginal Delivery of the Second Twin

 Vaginal Delivery of the Second Twin.    As soon as the first twin has been delivered, the presenting part of the second twin, size, and relationship to the birth canal are quickly ascertained by careful combined abdominal, vaginal, and at times intrauterine examination. Real-time sonography has proven quite valuable in some cases.

If the fetal head or the breech is fixed in the birth canal, moderate fundal pressure is applied and membranes are ruptured. Immediately afterward, the examination is repeated to identify prolapse of the cord. Labor is allowed to resume while the fetal heart rate is monitored. With reestablishment of labor there is no need to hasten delivery unless there is nonreassuring fetal heart rate or bleeding from the uterus. Hemorrhage from the uterus indicates placental separation, which can be deleterious to both the fetus and the mother. If contractions do not resume within approximately 10 minutes, dilute oxytocin may be used to stimulate appropriate myometrial activity, leading to spontaneous delivery or delivery assisted by outlet forceps.

If the occiput or the breech presents immediately over the pelvic inlet but is not fixed in the birth canal, the presenting part can often be guided into the pelvis with a vaginal hand while a hand on the uterine fundus exerts moderate pressure. Intrapartum external version of the noncephalic second twin has also been described (Chervenak and co-workers, 1983). Using the method shown in Figure 38–28 , the fetus who presents as breech or shoulder may be gently converted into a cephalic presentation. Once the presenting part is fixed in the pelvic inlet, membranes are ruptured and delivery is carried out as described earlier.

If the occiput or the breech is not over the pelvic inlet and cannot be so positioned by gentle pressure on the presenting part, or if the appreciable uterine bleeding develops, the problem of delivery of the second twin becomes serious. So as to take maximum advantage of the dilated cervix before the uterus contracts and the cervix retracts, procrastination must be avoided. An obstetrician skilled in intrauterine manipulation of the fetus and an anesthesiologist skilled in providing anesthesia that will effectively relax the uterus are essential for vaginal delivery with a favorable outcome. Prompt delivery of the second fetus by cesarean delivery is the better choice if there is no one present who is skilled in the performance of internal podalic version (described in the following section) or if anesthesia that will provide effective uterine relaxation is not immediately available.

Internal Podalic Version

 Internal Podalic Version.    In internal podalic version, the fetus is turned so as to deliver the feet first, which then enables the obstetrician to effect delivery by breech extraction. Chauhan and colleagues (1995) compared outcomes of 23 second twins delivered by breech extraction and podalic version with 21 who underwent external cephalic version (Fig. 38–28 ). Breech extraction was considered superior to external cephalic version because there was less fetal distress.

Through careful abdominal, vaginal, and intrauterine examinations, the various parts of the fetus can be identified. A hand is used to rupture the membranes and both feet are identified and grasped, and only then are they gently pulled toward the birth canal (Fig. 38–29 ). With the other hand applied to the abdomen, the head simultaneously is elevated gently (Fig. 38–30 ). An episiotomy is made or extended whenever more room is needed for uterine and vaginal manipulation. The legs are drawn slowly through the birth canal until the buttocks are visible anteriorly just beyond the maternal symphysis. A moist, warm towel is applied to the buttocks, and gentle traction is continued until the lower thirds of both scapulas are visible. Next, the trunk is slowly rotated with gentle traction until the shoulder and arm on one side of the fetus are delivered. Rotation of the fetal trunk now is gently reversed to deliver the other arm and shoulder into the vagina. The after-coming head may then be delivered either by simultaneous suprapubic external pressure to flex the head and gentle traction applied to the trunk, or by use of Piper forceps (see Chap. 21 , p. 502).

The cord is clamped promptly with two clamps on the placental side to identify it as the cord of the second infant. The placenta or placentas are delivered immediately by manual removal, if necessary. The uterus is promptly explored for defects and for retained pregnancy products. As these steps are being carried out, the uterine-relaxing anesthetic agent is discontinued, and as soon as uterine exploration has been completed, oxytocin is administered through an intravenous infusion system. Fundal massage or, preferably, manual compression of the uterus with one hand in the vagina against the lower uterine segment and the other transabdominally over the uterine fundus is applied to hasten and enhance myometrial contraction.

The cervix, vagina, periurethral region, vulva, and perineum are inspected carefully. Lacerations likely to bleed are repaired along with the episiotomy.

CESAREAN DELIVERY

 Cesarean Delivery.    Twin fetuses create unusual intraoperative problems. The mother is likely to be even less tolerant of the supine position, and therefore it is important to rotate her position so as to deflect the uterus to one side (see Chap. 8 , p. 209). In some cases, a vertical incision in the lower uterine segment may be advantageous. If a fetus lies transversely and the arms are inadvertently delivered first, it is much easier and safer to extend a vertical uterine incision upward than to extend a transverse incision.

It is important that the uterus be well contracted during completion of the cesarean delivery and thereafter. Remarkable blood loss may be concealed within the uterus and vagina and beneath the drapes during the time taken to close the incisions.

At times, attempts to deliver the second twin vaginally after delivery of the first twin not only may be unwise but also impossible. This may occur, for example, when the second fetus is much larger than the first, and is in a breech position or in a transverse lie. Even more perplexing, this may occur when the cervix promptly contracts and thickens after delivery of the first infant and does not dilate subsequently. Prompt cesarean delivery may be performed in these circumstances. Thompson and colleagues (1987) reported that 15 percent of second twins were delivered by cesarean section following vaginal delivery of the first twin. Of 29 such operations, 19 were for malpresentation, five for fetal distress, four for prolapsed cord, and one for arrested labor.

 DYSTOCIA

Dystocia is long, difficult, or abnormal labor; it is caused by various conditions associated with the five factors affecting labor. It is estimated that dystocia occurs in approximately 8% to 11% of women during the first stage of labor when the fetus is in a vertex presentation. Secondstage dystocia is equally as common (Wiznitzer, 1995). Dystocia can be caused by any of the following: • Dysfunctional labor, resulting in ineffective uterine contractions or maternal bearing-down efforts (the powers); the most common cause of dystocia (Cunningham et al., 2001) • Alterations in the pelvic structure (the passage) • Fetal causes, including abnormal presentation or position, anomalies, excessive size, and number of fetuses (the passenger) • Maternal position during labor and birth • Psychologic responses of the mother to labor related to past experiences, preparation, culture and heritage, and support system These factors are interdependent. In assessing the woman for an abnormal labor pattern, the nurse must consider consider the way in which these factors interact and influence labor progress. Dystocia is suspected when there is an alteration in the characteristics of uterine contractions, a lack of progress in the rate of cervical dilation, or a lack of progress in fetal descent and expulsion.

 

Dysfunctional  Labor

Dysfunctional labor is described as abnormal uterine contractions that prevent the normal progress of cervical dilation, effacement (primary powers), or descent (secondary powers). Dysfunction of uterine contractions can be further described as being hypertonic or hypotonic. Several factors seem to increase a woman's risk for uterine dystocia, including the following:

• Body build (e.g., 30 pounds or more overweight, short stature)

• Uterine abnormalities (e.g., congenital malformations, overdistention as with multiple gestation or hydramnios)

• Malpresentations and positions of the fetus

• Cephalopelvic disproportion

• Overstimulation with oxytocin

• Maternal fatigue, dehydration and electrolyte imbalance, and fear

• Inappropriate timing of analgesic or anesthetic administration

Research has also documented a familial occurrence of dystocia. Laboring women whose mothers or sisters experienced dystocia during their labors had an increased risk for experiencing dystocia themselves, possibly related to a genetic

factor affecting uterine activity (Berg-Lekas, Hogberg, & Winkvist, 1998).

 

Hypertonic uterine dysfunction

The woman experiencing hypertonic uterine dysfunction, or primary dysfunctional labor, often is an anxious first-time mother who is having painful and frequent contractions  that are ineffective in causing cervical dilation or effacement to progress. These contractions usually occur in the latent stage (cervical dilation of less than 4 cm) and are usually uncoordinated (Fig. 24-4). The force of the contractions may be in the midsection of the uterus rather than in the fundus, and the uterus is therefore unable to apply downward pressure to push the presenting part against the cervix. The uterus may not relax completely between contractions (Gilbert & Harmon, 1998; Varney, 1997). Women experiencing hypertonic uterine dysfunction may be exhausted and express concern about loss of control because of the intense pain they are experiencing and the  lack of progress. Therapeutic rest, which is achieved with a warm bath or shower and the administration of analgesicssuch as morphine, meperidine (Demerol), or nalbuphine(Nubain) to inhibit uterine contractions, reduce pain, and encourage sleep, is usually prescribed for the management of hypertonic uterine dysfunction. After a 4- to 6-hour rest these women are likely to awaken in active labor with a normal uterine contraction pattern (Gilbert & Harmon, 1998).

Alterations in pelvic structure

Pelvic dystocia. Pelvic dystocia can occur whenever there are contractures of the pelvic diameters that reduce the capacity of the bony pelvis, including the inlet, midpelvis, outlet, or any combination of these planes. Disproportion of the pelvis is the least common cause  of dystocia (Cunningham et al., 2001). Pelvic contractures may be caused by congenital abnormalities, maternal malnutrition, neoplasms, or lower spinal disorders. An immature pelvic size predisposes some adolescent mothers to pelvic dystocia. Pelvic deformities may also be the result of automobile or other accidents.

An inlet contracture is diagnosed whenever the diagonal conjugate is less than 11.5 cm. The incidence of face and shoulder presentation is increased. Because these presentations interfere with engagement and fetal descent, the risk of prolapse of the umbilical cord is increased. Inlet contracture is associated with maternal rickets and a flat pelvis. Weak uterine contractions may be noted during the first stage of labor in affected women. Midplane contracture, the most common cause of pelvic dystocia, is diagnosed whenever the sum of the interischial spinous and posterior sagittal diameters of the midpelvis is 13.5 cm or less. Fetal descent is arrested (transverse arrest of the fetal head) in such births because the head cannot rotate internally. These infants are usually born by cesarean, but vacuum-assisted birth has been used safely when the cervix is fully dilated. Midforceps-assisted birth usually is not done because of the increased perinatal morbidity associated with this intervention. Outlet contracture exists when the interischial diameter is 8 cm or less. It rarely occurs in the absence of midplane contracture. Women with outlet contracture have a long, narrow pubic arch and an android pelvis, and this causes fetal descent to be arrested. Maternal complications include extensive perineal lacerations during vaginal birth because the fetal head is pushed posteriorly.

Soft tissue dystocia. Soft tissue dystocia results from obstruction of the birth passage by an anatomic abnormality other than that involving the bony pelvis. The obstruction may result from placenta previa (low-lying placenta) that partially or completely obstructs the internal os of the cervix. Other causes, such as leiomyomas (uterine fibroids) in the lower uterine segment, ovarian tumors, and a full bladder or rectum, may prevent the fetus from entering the pelvis. Occasionally, cervical edema occurs during labor when the cervix is caught between the presenting part and the symphysis pubis or when the woman begins bearing-down efforts prematurely, thereby inhibiting complete dilation. Sexually transmitted infections (e.g., human papillomavirus) can alter cervical tissue integrity and thus interfere with adequate effacement and dilation. Bandl's ring, a pathologic retraction ring, is associated with prolonged rupture of membranes and protracted labor (Cunningham et al., 2001)

 

Fetal causes

Dystocia of fetal origin may be caused by anomalies, excessive fetal size and malpresentation, malposition, or multifetal pregnancy. Complications associated with dystocia of fetal origin include neonatal asphyxia, fetal injuries or fractures, and maternal vaginal lacerations. Although spontaneous vaginal birth is possible in these instances, a low-forceps-assisted, vacuum-assisted, or cesarean birth often is necessary. Anomalies. Gross ascites, large tumors, and open neural tube defects (e.g., myelomeningocele, hydrocephalus) are fetal anomalies that can cause dystocia. The  anomalies affect the relationship of the fetal anatomy to the maternal pelvic capacity, with the result that the fetus is unable to descend through the birth canal. Cephalopelvic disproportion. Cephalopelvic disproportion (CPD), also called fetopelvic disproportion, is related to excessive fetal size (i.e., 4000 g or more). It occurred at a rate of 18.3 per 1000 live births in 1999 (Ventura et al., 2001).

When CPD is present, the fetus cannot fit through the maternal pelvis to be born vaginally. Excessive fetal size, or macrosomia, is associated with maternal diabetes mellitus, obesity, multiparity, or the large size of one or both parents. If the maternal pelvis is too small, abnormally shaped, or deformed, CPD may be of maternal origin. In this case the fetus may be of average size or even smaller.

When CPD is present, the fetus cannot fit through the maternal pelvis to be born vaginally. Excessive fetal size, or macrosomia, is associated with maternal diabetes mellitus, obesity, multiparity, or the large size of one or both parents. If the maternal pelvis is too small, abnormally shaped, or deformed, CPD may be of maternal origin. In this case the fetus may be of average size or even smaller.

 

 

Unsatisfactory progress of labour

PROBLEMS

·                     The latent phase is longer than 8 hours.

·                     Cervical dilatation is to the right of the alert line on the partograph.

·                     The woman has been experiencing labour pains for 12 hours or more without delivery (prolonged labour).

GENERAL MANAGEMENT

·                     Make a rapid evaluation of the condition of the woman and fetus and provide supportive care.

·                     Test urine for ketones and treat with IV fluids if ketotic.

·                     Review partograph.

DIAGNOSIS 

TABLE S-10

 Diagnosis of unsatisfactory progress of labour 

Findings	Diagnosis
Cervix not dilated  No palpable contractions/infrequent contractions	False labour
Cervix not dilated beyond 4 cm after 8 hours of regular contractions	Prolonged latent phase
Cervical dilatation to the right of the alert line on the partograph (Fig S-6) • Secondary arrest of cervical dilatation and descent of presenting part in presence of good contractions • Secondary arrest of cervical dilatation and descent of presenting part with large caput, third degree moulding, cervix poorly applied to presenting part, oedematous cervix, ballooning of lower uterine segment, formation of retraction band, maternal and fetal distress (Fig S-7) • Less than three contractions in 10 minutes, each lasting less than 40 seconds (Fig S-8) • Presentation other than vertex with occiput anterior	Prolonged active phase • Cephalopelvic disproportion • Obstruction  • Inadequate uterine activity • Malpresentation or malposition
Cervix fully dilated and woman has urge to push, but there is no descent	Prolonged expulsive phase

 

Figure 6  is a sample partograph for prolonged active phase of labour:

 

·                     The woman was admitted in active labour at 10 AM:

- fetal head 5/5 palpable;

- cervix dilated 4 cm;

- inadequate contractions (two in 10 minutes, each lasting less than 20 seconds).

·                     At 2 PM:

- fetal head still 5/5 palpable;

- cervix dilated 4 cm and to the right of the alert line;

- membranes ruptured spontaneously and amniotic fluid is clear;

- inadequate uterine contractions (one in 10 minutes, lasting less than 20 seconds). 

·                     At 6 PM:

- fetal head still 5/5 palpable;

- cervix dilated 6 cm;

- contractions still inadequate (two in 10 minutes, each lasting less than 20 seconds).

·                     At 9 PM:

- fetal heart rate 80 per minute;

- amniotic fluid stained with meconium;

- no further progress in labour. 

·                     Caesarean section was performed at 9:20 PM due to fetal distress. 

·                     Note that the partograph was not adequately filled out. The diagnosis of prolonged labour was evident at 2 PM and labour should have been augmented with oxytocin at that time.

·                     FIGURE 6 Partograph showing prolonged active phase of labour 

 

 

Figure 7  is a sample partograph showing arrest of dilatation and descent in the active phase of labour. Fetal distress and third degree moulding together with arrest of dilatation and descent in the active phase of labour in the presence of adequate uterine contractions indicates obstructed labour.

·                     The woman was admitted in active labour at 10 AM:

- fetal head 3/5 palpable;

- cervix dilated 4 cm;

- three contractions in 10 minutes, each lasting 20–40 seconds;

- clear amniotic fluid draining;

- first degree moulding.

·                     At 2 PM:

- fetal head still 3/5 palpable;

- cervix dilated 6 cm and to the right of the alert line;

ght improvement in contractions (three in 10 minutes, each lasting 40 seconds);

- second degree moulding.

·                     At 5 PM:

- fetal head still 3/5 palpable;

- cervix still dilated 6 cm;

- third degree moulding;

- fetal heart rate 92 per minute.

·                     Caesarean section was performed at 5:30 PM.

 

Figure 8 is a sample partograph for poor progress of labour due to inadequate uterine contractions corrected with oxytocin.

·                     The woman was admitted in active labour at 10 AM:

- fetal head 5/5 palpable;

- cervix dilated 4 cm;

- two contractions in 10 minutes, each lasting less than 20 seconds. 

·                     At 12 PM:

- fetal head still 5/5 palpable;

- cervix still dilated 4 cm and to the right of the alert line;

- no improvement in contractions.

·                     At 2 PM:

- poor progress of labour due to inefficient uterine contractions diagnosed;

- augmented labour with oxytocin 10 units in 1 L IV fluids at 15 drops per minute;

- escalated oxytocin until a good pattern of contractions was established;

- contractions improved and were accompanied by descent of the presenting part and progressive cervical dilatation.

·                     Spontaneous vaginal delivery occurred at 8 PM.

FIGURE 8 Partograph showing inadequate uterine contractions corrected with oxytocin 

 

 

MANAGEMENT FALSE LABOUR

Examine for urinary tract or other infection (Table S-13) or ruptured membranes and treat accordingly. If none of these are present, discharge the woman and encourage her to return if signs of labour recur.

 

PROLONGED LATENT PHASE

The diagnosis of prolonged latent phase is made retrospectively. When contractions cease, the woman is said to have had false labour. When contractions become regular and dilatation progresses beyond 4 cm, the woman is said to have been in the latent phase.

Misdiagnosing false labour or prolonged latent phase leads to unnecessary induction or augmentation, which may fail. This may lead to unnecessary caesarean section and amnionitis. 

If a woman has been in the latent phase for more than 8 hours and there is little sign of progress, reassess the situation by assessing the cervix:

·                     If there has been no change in cervical effacement or dilatation and there is no fetal distress, review the diagnosis. The woman may not be in labour.

·                     If there has been a change in cervical effacement or dilatation, rupture the membranes with an amniotic hook or a Kocher clamp and induce labour using oxytocin or prostaglandins:

- Reassess every 4 hours;

- If the woman has not entered the active phase after 8 hours of oxytocin infusion, deliver by caesarean section.

·                     If there are signs of infection (fever, foul-smelling vaginal discharge):

- Augment labour immediately with oxytocin;

- Give a combination of antibiotics until delivery:

- ampicillin 2 g IV every 6 hours;

- PLUS gentamicin 5 mg/kg body weight IV every 24 hours;

- If the woman delivers vaginally, discontinue antibiotics postpartum;

- If the woman has a caesarean section, continue antibiotics PLUS give metronidazole 500 mg IV every 8 hours until the woman is fever-free for 48 hours.

 

 

PROLONGED ACTIVE PHASE

·                     If there are no signs of cephalopelvic disproportion or obstruction and the membranes are intact, rupture the membranes with an amniotic hook or a Kocher clamp.

·                     Assess uterine contractions:

- If contractions are inefficient (less than three contractions in 10 minutes, each lasting less than 40 seconds), suspect inadequate uterine activity(page S-66);

- If contractions are efficient (three contractions in 10 minutes, each lasting more than 40 seconds) suspect cephalopelvic disproportion, obstruction, malposition or
malpresentation (see below).

·                     General methods of labour support may improve contractions and accelerate progress.

 

 

CEPHALOPELVIC DISPROPORTION

Cephalopelvic disproportion occurs because the fetus is too large or the maternal pelvis is too small.  If labour persists with cephalopelvic disproportion, it may become arrested or obstructed. The best test to determine if a pelvis is adequate is a trial of labour. Clinical pelvimetry is of limited value.

·                     If cephalopelvic disproportion is confirmed (Table S-10), deliver by caesarean section.

·                     If the fetus is dead:

- Deliver by craniotomy;

- If the operator is not proficient in craniotomy, deliver by ccaesarean section.

 

 

OBSTRUCTION

Note: Rupture of an unscarred uterus is usually caused by obstructed labour.

·                     If the fetus is alive, the cervix is fully dilated and the head is at 0 station or below, deliver by vacuum extraction;

·                     If there is an indication for vacuum extraction and symphysiotomy for relative obstruction and the fetal head is at -2 station:

- Deliver by vacuum extraction and symphysiotomy;

- If the operator is not proficient in symphysiotomy, deliver by caesarean section.

·                     If the fetus is alive but the cervix is not fully dilated or if the fetal head is too high for vacuum extraction, deliver by caesarean section.

·                     If the fetus is dead:

- Deliver by craniotomy;

- If the operator is not proficient in craniotomy, deliver by caesarean section.

 

INADEQUATE UTERINE ACTIVITY

If contractions are inefficient and cephalopelvic disproportion and obstruction have been excluded, the most probable cause of prolonged labour is inadequate uterine activity.

Inefficient contractions are less common in a multigravida than in a primigravida. Hence, every effort should be made to rule out disproportion in a multigravida before augmenting with oxytocin. 

·                     Rupture the membranes with an amniotic hook or a Kocher clamp and augment labour using oxytocin.

·                     Reassess progress by vaginal examination 2 hours after a good contraction pattern with strong contractions has been established:

- If there is no progress between examinations, deliver by caesarean section;

- If progress continues, continue oxytocin infusion and re-examine after 2 hours. Continue to follow progress carefully.

 

PROLONGED EXPULSIVE PHASE

Maternal expulsive efforts increase fetal risk by reducing the delivery of oxygen to the placenta. Allow spontaneous maternal “pushing”, but do not encourage prolonged effort and holding the breath.

·                     If malpresentation and obvious obstruction have been excluded, augment labour with oxytocin. 

·                     If there is no descent after augmentation:

- If the head is not more than 1/5 above the symphysis pubis or the leading bony edge of the fetal head is at 0 station, deliver by vacuum extraction or forceps;

- If the head is between 1/5 and 3/5 above the symphysis pubis or the leading bony edge of the fetal head is between 0 station and -2 station:

- Deliver by vacuum extraction and symphysiotomy;

- If the operator is not proficient in symphysiotomy, deliver by caesarean section.

- If the head is more than 3/5 above the symphysis pubis or the leading bony edge of the fetal head is above -2 station, deliver by caesarean section.

 

 Diagnosis of unsatisfactory progress of labour 

Findings	Diagnosis
Cervix not dilated  No palpable contractions/infrequent contractions	False labour
Cervix not dilated beyond 4 cm after 8 hours of regular contractions	Prolonged latent phase
Cervical dilatation to the right of the alert line on the partograph (Fig S-6) • Secondary arrest of cervical dilatation and descent of presenting part in presence of good contractions • Secondary arrest of cervical dilatation and descent of presenting part with large caput, third degree moulding, cervix poorly applied to presenting part, oedematous cervix, ballooning of lower uterine segment, formation of retraction band, maternal and fetal distress (Fig S-7) • Less than three contractions in 10 minutes, each lasting less than 40 seconds (Fig S-8) • Presentation other than vertex with occiput anterior	Prolonged active phase • Cephalopelvic disproportion • Obstruction  • Inadequate uterine activity • Malpresentation or malposition
Cervix fully dilated and woman has urge to push, but there is no descent	Prolonged expulsive phase

 

Labour with an overdistended uterus

PROBLEM

·         A woman in labour has an overdistended uterus or symphysis-fundal height more than expected for the period of gestation. 

GENERAL MANAGEMENT

·         Prop up the woman.

·         Confirm accuracy of calculated gestational age, if possible.

DIAGNOSIS

·         If only one fetus is felt on abdominal examination, consider wrong dates, a single large fetus  or an excess of amniotic fluid.

·         If multiple fetal poles and parts are felt on abdominal examination, suspect multiple pregnancy. Other signs of multiple pregnancy include:

- fetal head small in relation to the uterus;

- uterus larger than expected for gestation;

- more than one fetal heart heard with Doppler fetal stethoscope. 

Note: An acoustic fetal stethoscope cannot be used to confirm the diagnosis, as one heart may be heard in different areas. 

·         Use ultrasound examination, if available, to:

- identify the number, presentations and sizes of fetuses;

- assess the volume of amniotic fluid.

·         If ultrasound service is not available, perform radiological examination (anterio-posterior view) for number of fetuses and presentations.

MANAGEMENT 

SINGLE LARGE FETUS

·         Manage as for normal labour. 

·         Anticipate and prepare for prolonged and obstructed labour, shoulder dystocia and postpartum haemorrhage.

EXCESS AMNIOTIC FLUID

·         Allow labour to progress and monitor progress using a partograph.

·         If the woman is uncomfortable because of uterine distension, aspirate excess amniotic fluid:

- Palpate for location of fetus;

- Prepare the skin with an antiseptic;

- Under aseptic conditions, insert a 20-gauge spinal needle through the abdominal and uterine walls and withdraw the stylet;

- Aspirate the fluid using a large syringe. Alternatively, attach an infusion set to the needle and allow the fluid to slowly drain into a container;

- When the woman is no longer distressed because of overdistension, replace the stylet and remove the needle.

·         If rupture of membranes is indicated for other reasons, rupture the membranes with an amniotic hook or a Kocher clamp.

·         Check for cord prolapse when membranes rupture. If the cord prolapses and delivery is not imminent, deliver by caesarean section.

MULTIPLE PREGNANCY

FIRST BABY

·         Start an IV infusion and slowly infuse IV fluids.

·         Monitor fetuses by intermittent auscultation of the fetal heart rates. If there are fetal heart rate abnormalities (less than 100 or more than 180 beats per minute), suspect fetal distress.

·         Check presentation:

- If a vertex presentation, allow labour to progress as for a single vertex presentation and monitor progress in labour using a partograph;

- If a breech presentation, apply the same guidelines as for a singleton breech presentation and monitor progress in labour using a partograph;

- If a transverse lie, deliver by caesarean section.

Leave a clamp on the maternal end of the umbilical cord and do not attempt to deliver the placenta until the last baby is delivered. 

SECOND OR ADDITIONAL BABY(S) 

·         Immediately after the first baby is delivered:

- Palpate the abdomen to determine lie of additional baby;

- Correct to longitudinal lie by external version;

- Check fetal heart rate(s).

·         Perform a vaginal examination to determine if:

- cord has prolapsed;

- the membranes are intact or ruptured.

VERTEX PRESENTATION

·         If the head is not engaged, manoeuvre the head into the pelvis manually (hands on abdomen), if possible.

·         If the membranes are intact, rupture the membranes with an amniotic hook or a Kocher clamp.

·         Check fetal heart rate between contractions.

·         If contractions are inadequate after birth of first baby, augment labour with oxytocin using rapid escalation (Table P-8, page P-23) to produce good contractions (three contractions in 10 minutes, each lasting more than 40 seconds).

·         If spontaneous delivery does not occur within 2 hours of good contractions or if there are fetal heart rate abnormalities (less than 100 or more than 180 beats per minute), deliver by caesarean section.

 

BREECH PRESENTATION

·         If the baby is estimated to be no larger than the first baby, and if the cervix has not contracted, consider vaginal delivery:

- If there are inadequate or no contractions after birth of first baby, escalate oxytocin infusion at a rapid rate (Table P-8) to produce good contractions (three contractions in 10 minutes, each lasting more than 40 seconds);

- If the membranes are intact and the breech has descended, rupture the membranes with an amniotic hook or a Kocher clamp;

- Check fetal heart rate between contractions. If there are fetal heart rate abnormalities (less than 100 or more than 180 beats per minute), deliver by breech extraction;

• If vaginal delivery is not possible, deliver by caesarean section.

TRANSVERSE LIE

·         If the membranes are intact, attempt external version;

·         If external version fails and the cervix is fully dilated and membranes are still intact, attempt internal podalic version:

Note: Do not attempt internal podalic version if the provider is untrained, the membranes have ruptured and the amniotic fluid has drained, or if the uterus is scarred. Do not persist if the baby does not turn easily.

- Wearing high-level disinfected gloves, insert a hand into the uterus and grasp the baby’s foot;

- Gently rotate the baby down;

- Proceed with breech extraction.

·         Check fetal heart rate between contractions;

• If external version fails and internal podalic version is not advisable or fails, deliver by caesarean section.

·         Give oxytocin 10 units IM or give ergometrine 0.2 mg IM within 1 minute after delivery of the last baby and continue active management of the third stage toreduce postpartum blood loss. 

COMPLICATIONS

·         Maternal complications of multiple pregnancy include:

- anaemia;

- abortion;

- pregnancy-induced hypertension and pre-eclampsia;

- excess amniotic fluid;

- poor contractions during labour;

- retained placenta;

- postpartum haemorrhage.

·         Placental/fetal complications include:

- placenta praevia;

- abruptio placentae;

- placental insufficiency;- preterm delivery;

- low birth weight;

- malpresentations;

- cord prolapse;

- congenital anomalies.