PHYSIOLOGY OF DELIVERY. ANESTHESIA IN LABOR. PHYSIOLOGY OF POST-NATAL PERIOD. PHYSIOLOGY OF INFANTS’ PERIOD
Prepared by N. Bahnij
CLINICAL COURSE OF LABOR
The last few hours of human pregnancy are characterized by uterine contractions that effect dilatation of the cervix and force the fetus through the birth canal. Much energy is expended during this time; hence the use of the term labor to describe this process. The myometrial contractions of labor are painful, which is why the term labor pains is used to describe this process.
Before these forceful, painful contractions begin, however, the uterus must be prepared for labor. During the first 36 to 38 weeks of gestation, the myometrium is unresponsive; after this prolonged period of quiescence, a transitional phase is required during which myometrial unresponsiveness is suspended and the cervix is softened and effaced. Indeed, there are multiple functional states of the uterus that must be implemented during pregnancy and the puerperium; these are described later and categorized as the uterine phases of parturition.
Myometrial contractions that do not cause cervical dilatation may be observed at any time during pregnancy. These contractions are characterized by unpredictability in occurrence, lack of intensity, and brevity of duration. Any discomfort that they produce is usually confined to the lower abdomen and groin. Near the end of pregnancy, as the uterus undergoes preparation for labor, contractions of this type are more common, especially in multiparas, and sometimes are referred to as false labor. In some women, however, the forceful uterine contractions that effect cervical dilatation, fetal descent, and delivery of the conceptus begin suddenly, seemingly without warning.
ANATOMICAL AND PHYSIOLOGICAL CONSIDERATIONS. There are unique characteristics of myometrial muscle (and other smooth muscles) compared with skeletal muscle. Huszar and Walsh (1989) point out that these differences create a peculiar advantage for the myometrium in the efficiency of uterine contractions and the delivery of the fetus. First, the degree of shortening of smooth muscle cells with contractions may be one order of magnitude greater than that attained in striated muscle cells. Second, forces can be exerted in smooth muscle cells in any direction, whereas the contraction force generated by skeletal muscle is always aligned with the axis of the muscle fibers. Third, smooth muscle is not organized in the same manner as skeletal muscle; in myometrium, the thick and thin filaments are found in long, random bundles throughout the cells. This arrangement facilitates greater shortening and force-generating capacity of smooth muscle. Fourth, there is the advantage that multidirectional force generation in myometrial smooth muscle permits versatility in expulsive force directionality that can be brought to bear irrespective of the lie or presentation of the fetus.
BIOCHEMISTRY OF SMOOTH MUSCLE CONTRACTIONS. The interaction of myosin and actin is essential to muscle contraction. Myosin (Mr about 500,000) is comprised of multiple light and heavy chains and is laid down in thick myofilaments. The interaction of myosin and actin, which causes activation of ATPase, ATP hydrolysis, and force generation, is effected by enzymatic phosphorylation of the 20-kd light chain of myosin (Stull and colleagues, 1988, 1998). This phosphorylation reaction is catalyzed by the enzyme myosin light chain kinase, which is activated by Ca2+ (Fig. 11-1).
Ca2+ binds to calmodulin, a calcium-binding regulatory protein, which in turn binds to and activates myosin light chain kinase. In this manner, agents that act on myometrial smooth muscle cells to cause an increase in the intracellular cytosolic concentration of calcium ([Ca2+]i) promote contraction. Conditions that cause a decrease in [Ca2+]i favor relaxation. Ordinarily, agents that cause an increase in the intracellular concentration of cyclic adenosine monophosphate (cAMP) or cyclic guanosine monophosphate (cGMP) promote uterine relaxation. It is believed that cAMP and cGMP act to cause a decrease in [Ca2+]i, although the exact mechanism(s) is not defined. The biochemistry and physiology of smooth muscle contractility have been reviewed by Barany and Barany (1990) and by Sanborn and colleagues (1994).
THE THREE STAGES OF LABOR. Active labor is divided into three separate stages.
The first stage of labor begins when uterine contractions of sufficient frequency, intensity, and duration are attained to bring about effacement and progressive dilatation of the cervix. The first stage of labor ends when the cervix is fully dilated, that is, when the cervix is sufficiently dilated (about 10 cm) to allow passage of the fetal head. The first stage of labor, therefore, is the stage of cervical effacement and dilatation.
The second stage of labor begins when dilatation of the cervix is complete, and ends with delivery of the fetus. The second stage of labor is the stage of expulsion of the fetus.
The third stage of labor begins immediately after delivery of the fetus, and ends with the delivery of the placenta and fetal membranes. The third stage of labor is the stage of separation and expulsion of the placenta.
CLINICAL ONSET OF LABOR. A rather dependable sign of the impending onset of active labor (provided rectal or vaginal examinations have not been performed in the preceding 48 hours) is the discharge of a small amount of blood-tinged mucus from the vagina. This represents the extrusion of the plug of mucus that had filled the cervical canal during pregnancy, and is referred to as "show" or "bloody show." This is a late sign, because commonly labor is already in progress or likely will ensue during the next several hours to few days. Normally, only a few drops of blood escape with the mucus plug; more substantial bleeding is suggestive of an abnormal cause.
UTERINE CONTRACTIONS CHARACTERISTIC OF LABOR. Unique among physiological muscular contractions, those of uterine smooth muscle of labor are painful. The cause of the pain is not known definitely, but several possibilities have been suggested:
1. Hypoxia of the contracted myometrium (as in angina pectoris).
2. Compression of nerve ganglia in the cervix and lower uterus by the interlocking muscle bundles.
3. Stretching of the cervix during dilatation.
4. Stretching of the peritoneum overlying the fundus.
Compression of nerve ganglia in the cervix and lower uterine segment by the contracting myometrium is an especially attractive hypothesis. Paracervical infiltration with a local anesthetic usually produces appreciable relief of pain during subsequent uterine contractions
Uterine contractions are involuntary and, for the most part, independent of extrauterine control. Neural blockage from epidural analgesia does not diminish the frequency and intensity of uterine contractions. Moreover, the myometrial contractions in paraplegic women are normal, though painless, as in women after bilateral lumbar sympathectomy.
Mechanical stretching of the cervix enhances uterine activity in several species, including humans. This phenomenon has been referred to as the Ferguson reflex (1941). The exact mechanism by which mechanical dilatation of the cervix causes increased myometrial contractility is not clear. Release of oxytocin was suggested as the cause, but this is not proven. Manipulation of the cervix and "stripping" the fetal membranes is associated with an increase in the levels of prostaglandin F2a metabolite (PGFM) in blood .
The interval between contractions diminishes gradually from about 10 minutes at the onset of the first stage of labor to as little as 1 minute or less in the second stage. Periods of relaxation between contractions, however, are essential to the welfare of the fetus. Unremitting contraction of the uterus compromises uteroplacental blood flow, and ultimately, fetal-placental flow, sufficiently to cause fetal hypoxemia. In the active phase of labor, the duration of each contraction ranges from 30 to 90 seconds, averaging about 1 minute. There is appreciable variability in the intensity of uterine contractions during apparently normal labor, as emphasized by Schulman and Romney (1970). They recorded the amnionic fluid pressures generated by uterine contractions during spontaneous labor; the average was about 40 mm Hg, but varied from 20 to 60 mm Hg (Chap. 14, p. 355).
DIFFERENTIATION OF UTERINE ACTIVITY. During active labor, the uterus is transformed into two distinct parts. The actively contracting upper segment becomes thicker as labor advances. The lower portion, comprising the lower segment of the uterus and the cervix, is relatively passive compared with the upper segment, and it develops into a much more thinly walled passage for the fetus. The lower uterine segment is analogous to a greatly expanded and thinned-out isthmus of the uterus of nonpregnant women, the formation of which is not solely a phenomenon of labor. The lower segment develops gradually as pregnancy progresses and then thins remarkably during labor (Figs. 11-2 and 11-3). By abdominal palpation, even before rupture of the membranes, the two segments can be differentiated during a contraction. The upper uterine segment is quite firm or hard, whereas the consistency of the lower uterine segment is much less firm. The former is the actively contracting part of the uterus; the latter is the distended, normally much more passive, portion.
If the entire wall of uterine musculature, including the lower uterine segment and cervix, were to contract simultaneously and with equal intensity, the net expulsive force would be decreased markedly. Herein lies the importance of the division of the uterus into an actively contracting upper segment and a more passive lower segment that differ not only anatomically but also physiologically. The upper segment contracts, retracts, and expels the fetus; in response to the force of the contractions of the upper segment, the softened lower uterine segment and cervix dilate and thereby form a greatly expanded, thinned-out muscular and fibromuscular tube through which the fetus can be extruded.
The myometrium of the upper uterine segment does not relax to its original length after contractions; rather, it becomes relatively fixed at a shorter length. The tension, however, remains the same as before the contraction. The upper portion of the uterus, or active segment, contracts down on its diminishing contents, but myometrial tension remains constant. The net effect is to take up slack, maintaining the advantage gained in the expulsion of the fetus, and keeping the uterine musculature in firm contact with the intrauterine contents. As the consequence of retraction, each successive contraction commences where its predecessor left off, so that the upper part of the uterine cavity becomes slightly smaller with each successive contraction. Because of the successive shortening of the muscular fibers with contractions, the upper active uterine segment becomes progressively thickened throughout the first and second stages of labor and tremendously thickened immediately after delivery of the fetus (Fig. 11-2). The phenomenon of retraction of the upper uterine segment is contingent upon a decrease in the volume of its contents. For the contents to be diminished, particularly early in labor when the entire uterus is virtually a closed sac with only a minute opening at the cervical os, the musculature of the lower segment must stretch. This permits increasingly more of the intrauterine contents to occupy the lower segment, and the upper segment retracts only to the extent that the lower segment distends and the cervix dilates.
The relaxation of the lower uterine segment is not a complete relaxation, but rather the opposite of retraction. The fibers of the lower segment become stretched with each contraction of the upper segment, after which these are not returned to the previous length but rather remain relatively fixed at the longer length; the tension, however, remains essentially the same as before. The musculature still manifests tone, still resists stretch, and still contracts somewhat on stimulation. The successive lengthening of the muscular fibers in the lower uterine segment, as labor progresses, is accompanied by thinning, normally to only a few millimeters in the thinnest part. As a result of the thinning of the lower uterine segment and the concomitant thickening of the upper, the boundary between the two is marked by a ridge on the inner uterine surface, the physiological retraction ring. When the thinning of the lower uterine segment is extreme, as in obstructed labor, the ring is very prominent, forming a pathological retraction ring. This is an abnormal condition also known as Bandl ring, which is illustrated in Figure 11-2 and discussed further in Chapter 18 (p. 443). The existence of a gradient of diminishing physiological activity from fundus to cervix was established from measurements of differences in behavior of the upper and lower parts of the uterus during normal labor.
CHANGE IN UTERINE SHAPE. Each contraction produces an elongation of the uterine ovoid with a concomitant decrease in horizontal diameter. By virtue of this change in shape, there are important effects on the process of labor. First, the decrease in horizontal diameter produces a straightening of the fetal vertebral column, pressing its upper pole firmly against the fundus of the uterus, whereas the lower pole is thrust farther downward and into the pelvis. The lengthening of the fetal ovoid thus produced has been estimated as between 5 and 10 cm. The pressure exerted in this fashion is known as the fetal axis pressure. Second, with lengthening of the uterus, the longitudinal fibers are drawn taut and because the lower segment and cervix are the only parts of the uterus that are flexible, these are pulled upward over the lower pole of the fetus. This effect on the musculature of the lower segment and on the cervix is an important factor in cervical dilatation.
ANCILLARY FORCES IN LABOR. After the cervix is dilated fully, the most important force in the expulsion of the fetus is that produced by increased maternal intra-abdominal pressure. This is created by contraction of the abdominal muscles simultaneously with forced respiratory efforts with the glottis closed. This is referred to as "pushing." The nature of the force produced is similar to that involved in defecation, but the intensity usually is much greater. The importance of intra-abdominal pressure in fetal expulsion is most clearly attested to by the labors of women who are paraplegic. Such women suffer no pain, although the uterus may contract vigorously. Cervical dilatation, in large measure the result of uterine contractions acting on a softened cervix, proceeds normally, but expulsion of the infant is accomplished more readily when the woman is instructed to bear down and can do so during a uterine contraction.
Although increased intra-abdominal pressure is required for the spontaneous completion of labor, it is futile until the cervix is fully dilated. Specifically, it is a necessary auxiliary to uterine contractions in the second stage of labor, but pushing accomplishes little in the first stage, except to produce fatigue. Intra-abdominal pressure also may be important in the third stage of labor, especially if the parturient is unattended. After the placenta has separated, its spontaneous expulsion is aided by the mother increasing intra-abdominal pressure.
Before the onset of labor, during the phase of uterine awakening and preparedness, the cervix is softened, which facilitates dilatation of the cervix once forceful myometrial contractions of labor begin.
CHANGES INDUCED IN THE CERVIX WITH LABOR. The effective force of the first stage of labor is the uterine contraction, which in turn exerts hydrostatic pressure through the fetal membranes against the cervix and lower uterine segment. In the absence of intact membranes, the fetal presenting part is forced directly against the cervix and lower uterine segment. As the result of the action of these forces, two fundamental changes—effacement and dilatation—take place in the already softened cervix. For the head of the average fetus at term to pass through the cervix, the cervical canal must dilate to a diameter of about 10 cm; at this time, the cervix is said to be completely (or fully) dilated. There may be no fetal descent during cervical effacement, but most commonly the presenting fetal part descends somewhat as the cervix dilates. During the second stage of labor, descent of the fetal presenting part typically occurs rather slowly but steadily in nulliparas. In multi-paras, however, particularly those of high parity, descent may be very rapid.
The "obliteration" or "taking up" of the cervix is the shortening of the cervical canal from a length of about 2 cm to a mere circular orifice with almost paper-thin edges. This process is referred to as effacement and takes place from above downward. The muscular fibers at about the level of the internal cervical os are pulled upward, or "taken up," into the lower uterine segment, as the condition of the external os remains temporarily unchanged. The edges of the internal os are drawn upward several centimeters to become a part (both anatomically and functionally) of the lower uterine segment. Effacement may be compared with a funneling process in which the whole length of a narrow cylinder is converted into a very obtuse, flaring funnel with a small circular orifice for an outlet. As the result of increased myometrial activity during uterine preparedness for labor, appreciable effacement of the softened cervix sometimes is accomplished before active labor begins. Effacement causes expulsion of the mucus plug as the cervical canal is shortened.
Compared with the body of the uterus, the lower uterine segment and the cervix are regions of lesser resistance. Therefore, during a contraction, these structures are subjected to distention, in the course of which a centrifugal pull is exerted on the cervix. As the uterine contractions cause pressure on the membranes, the hydrostatic action of the amnionic sac in turn dilates the cervical canal like a wedge. In the absence of intact membranes, the pressure of the presenting part against the cervix and lower uterine segment is similarly effective. Early rupture of the membranes does not retard cervical dilatation so long as the presenting part of the fetus is positioned to exert pressure against the cervix and lower uterine segment. The process of cervical effacement and dilatation causes the formation of the forebag of the amnionic fluid, which is later described in detail.
PATTERN OF CERVICAL DILATATION. Friedman, in his treatise on labor (1978), stated that "the clinical features of uterine contractions—namely, frequency, intensity, and duration—cannot be relied upon as measures of progression in labor nor as indices of normality. ... Except for cervical dilatation and fetal descent, none of the clinical features of the parturient... appears to be useful in assessing labor progression." The pattern of cervical dilatation that takes place during the course of normal labor takes on the shape of a sigmoid curve. As depicted in Figure 11-11, two phases of cervical dilatation are the latent phase and the active phase. The active phase has been subdivided further as the acceleration phase, the phase of maximum slope, and the deceleration phase (Friedman, 1978). The duration of the latent phase is more variable and subject to sensitive changes by extraneous factors and by sedation (prolongation of latent phase) and myometrial stimulation (shortening of latent phase). The duration of the latent phase has little bearing on the subsequent course of labor, whereas the characteristics of the accelerated phase are usually predictive of the outcome of a particular labor. Friedman considers the maximum slope as a "good measure of the overall efficiency of the machine," whereas the nature of the deceleration phase is more reflective of fetopelvic relationships. The completion of cervical dilatation during the active phase of labor is accomplished by cervical retraction about the presenting part of the fetus. After complete cervical dilatation, the second stage of labor commences; thereafter, only progressive descent of the presenting fetal part is available to assess the progress of labor.
PATTERN OF FETAL DESCENT. In many nulliparas, engagement of the fetal head is accomplished before labor begins, and further descent does not occur until late in labor. In others in which engagement of the fetal head is initially not so complete, further descent occurs during the first stage of labor. In the descent pattern of normal labor, a typical hyperbolic curve is formed when the station of the fetal head is plotted as a function of the duration of labor. Active descent usually takes place after cervical dilatation has progressed for some time (Fig. 11-12). In nulliparas, increased rates of descent are observed ordinarily during the phase of maximum slope of cervical dilatation. At this time, the speed of descent increases to a maximum, and this maximal rate of descent is maintained until the presenting fetal part reaches the perineal floor (Friedman, 1978).
CRITERIA FOR NORMAL LABOR. Friedman also sought to select criteria that would delimit normal labor and thereby enable identification of significant abnormalities in labor. The limits, admittedly arbitrary, appear to be logical and clinically useful. The group of women studied were nulliparas and multiparas with no fetopelvic disproportion, no fetal malposition or malpresentation, no multiple pregnancy, and none were treated with heavy sedation or conduction analgesia, oxytocin, or operative intervention. All had a normal pelvis, were at term with a vertex presentation, and delivered average-sized infants. From these studies, Friedman developed the concept of three functional divisions of labor—preparatory, dilatational, and pelvic—to describe the physiological objectives of each division. He found that the preparatory division of labor may be sensitive to sedation and conduction analgesia. Although little cervical dilatation occurs during this time, considerable changes take place in the extracellular matrix (collagen and other connective tissue components) of the cervix. The dilatational division of labor, during which time dilatation is occurring at the most rapid rate, is principally unaffected by sedation or conduction analgesia. The pelvic division of labor begins with the deceleration phase of cervical dilatation. The classical mechanisms of labor, which involve the cardinal movements of the fetus, take place principally during the pelvic division of labor. The onset of the pelvic division is seldom clinically identifiable separate from the dilatational division of labor. Moreover, the rate of cervical dilatation does not always decelerate as full dilatation is approached; in fact, it may accelerate.
RUPTURE OF THE MEMBRANES. Spontaneous rupture of the membranes most often occurs sometime during the course of active labor. Typically, rupture is evident by a sudden gush of a variable quantity of normally clear or slightly turbid, nearly colorless fluid. Less frequently, the membranes remain intact until delivery of the infant. If by chance the membranes remain intact until completion of delivery, the fetus is born surrounded by them, and the portion covering the head of the newborn infant is sometimes referred to as the caul. Rupture of the membranes before the onset of labor at any stage of gestation is referred to as premature rupture of the membranes.
CHANGES IN THE VAGINA AND PELVIC FLOOR.
The birth canal is supported and is functionally closed by a number of layers of tissues that together form the pelvic floor. Its most important structures are the levator ani muscle and the fascia covering its upper and lower surfaces, which for practical purposes may be considered as the pelvic floor (Chap. 3). This group of muscles closes the lower end of the pelvic cavity as a diaphragm and thereby a concave upper and a convex lower surface is presented (see Fig. 3-6). On either side, the levator ani consists of a pubococcygeus and iliococcygeus portion. The posterior and lateral portions of the pelvic floor, which are not filled out by the levator ani, are occupied by the piriformis and coccygeus muscles on either side.
The levator ani varies in thickness from 3 to 5 mm, though its margins encircling the rectum and vagina are somewhat thicker. During pregnancy, the levator ani usually undergoes hypertrophy. By vaginal examination, the internal margin of this muscle can be felt as a thick band that extends backward from the pubis and encircles the vagina about 2 cm above the hymen. On contraction, the levator ani draws both the rectum and vagina forward and upward in the direction of the symphysis pubis and thereby acts to close the vagina. The more superficial muscles of the perineum are too delicate to serve more than an accessory function.
In the first stage of labor, the membranes and presenting part of the fetus serve a role in dilating the upper portion of the vagina. After the membranes have ruptured, however, the changes in the pelvic floor are caused entirely by pressure exerted by the fetal presenting part. The most marked change consists of the stretching of the fibers of the levator ani muscles and the thinning of the central portion of the perineum, which becomes transformed from a wedge-shaped mass of tissue 5 cm in thickness to (in the absence of an episiotomy) a thin, almost transparent membranous structure less than 1 cm in thickness. When the perineum is distended maximally, the anus becomes markedly dilated and presents an opening that varies from 2 to 3 cm in diameter and through which the anterior wall of the rectum bulges. The extraordinary number and size of the blood vessels that supply the vagina and pelvic floor effects a great increase in the amount of blood loss when these tissues are torn.
The third stage of labor begins immediately after delivery of the fetus and involves the separation and expulsion of the placenta. After delivery of the placenta and fetal membranes, active labor is completed. As the baby is born, the uterus spontaneously contracts down on its diminishing contents. Normally, by the time the infant is completely delivered, the uterine cavity is nearly obliterated and the organ consists of an almost solid mass of muscle, several centimeters thick above the thinner lower segment. The uterine fundus now lies just below the level of the umbilicus. This sudden diminution in uterine size is inevitably accompanied by a decrease in the area of the placental implantation site (Fig. 11-13). For the placenta to accommodate itself to this reduced area, it increases in thickness, but because of limited placental elasticity, it is forced to buckle. The resulting tension causes the weakest layer of the decidua—the spongy layer, or decidua spongiosa—to give way, and cleavage takes place at that site. Therefore, separation of the placenta results primarily from a disproportion created between the unchanged size of the placenta and the reduced size of the underlying implantation site. During cesarean delivery, this phenomenon may be directly observed when the placenta is implanted posteriorly.
Cleavage of the placenta is greatly facilitated by the nature of the loose structure of the spongy decidua, which may be likened to the row of perforations between postage stamps. As separation proceeds, a hematoma forms between the separating placenta and the remaining decidua. Formation of the hematoma is usually the result, rather than the cause, of the separation, because in some cases bleeding is negligible. The hematoma may, however, accelerate the process of cleavage. Because the separation of the placenta is through the spongy layer of the decidua, part of the decidua is cast off with the placenta, whereas the rest remains attached to the myometrium. The amount of decidual tissue retained at the placental site varies.
Placental separation ordinarily occurs within a very few minutes after delivery. Brandt (1933) and others, based on results obtained in combined clinical and radiographic studies, supported the idea that because the periphery of the placenta is probably the most adherent portion, separation usually begins elsewhere. Occasionally some degree of separation begins even before the third stage of labor, probably accounting for certain cases of fetal heart rate decelerations that occur just before expulsion of the infant.
SEPARATION OF AMNIOCHORION.
The great decrease in the surface area of the cavity of the uterus simultaneously causes the fetal membranes (amniochorion) and the parietal decidua to be thrown into innumerable folds that increase the thickness of the layer from less than 1 mm to 3 to 4 mm. The lining of the uterus early in the third stage indicates that much of the parietal layer of decidua parietalis is included between the folds of the festooned amnion and chorion laeve (Fig. 11-14). The membranes usually remain in situ until the separation of the placenta is nearly completed. These are then peeled off the uterine wall, partly by the further contraction of the myometrium and partly by traction that is exerted by the separated placenta, which lies in the thin lower uterine segment or in the upper portion of the vagina. The body of the uterus at that time normally forms an almost solid mass of muscle, the anterior and posterior walls of which, each measuring 4 to 5 cm in thickness, lie in close apposition such that the uterine cavity is almost obliterated.
After the placenta has separated from its implantation site, the pressure exerted upon it by the uterine walls causes it to slide downward into the lower uterine segment or the upper part of the vagina. In some cases the placenta may be expelled from those locations by an increase in abdominal pressure, but women in the recumbent position frequently cannot expel the placenta spontaneously. An artificial means of completing the third stage is therefore generally required. The usual method employed is alternately to compress and elevate the fundus, while exerting minimal traction on the umbilical cord .
MECHANISMS OF PLACENTAL EXTRUSION.
When the central, or usual, type of placental separation occurs, the retroplacental hematoma is believed to push the placenta toward the uterine cavity, first the central portion and then the rest. The placenta, thus inverted and weighted with the hematoma, then descends. Because the surrounding membranes are still attached to the decidua, the placenta can descend only by dragging the membranes along; the membranes then peel off its periphery. Consequently, the sac formed by the membranes is inverted, with the glistening amnion over the placental surface presenting at the vulva. The retroplacental hematoma either follows the placenta or is found within the inverted sac. In this process, known as the Schultze mechanism of placental expulsion, blood from the placental site pours into the inverted sac, not escaping externally until after extrusion of the placenta. The other method of placental extrusion is known as the Duncan mechanism, in which separation of the placenta occurs first at the periphery, with the result that blood collects between the membranes and the uterine wall and escapes from the vagina. In this circumstance, the placenta descends to the vagina sideways, and the maternal surface is the first to appear at the vulva.
PHYSIOLOGICAL AND BIOCHEMICAL PROCESSES OF PARTURITION
The physiological processes in human pregnancy that results in the initiation of parturition and the onset of labor are not defined. Until recently, it was generally accepted that successful pregnancy in all mammalian species was dependent upon the action of progesterone to maintain uterine quiescence until near the end of gestation. This assumption was supported by the finding that in the majority of mammalian pregnancies studied, progesterone withdrawal (whether naturally occurring or surgically or pharmacologically induced) precedes the initiation of parturition. In many of these species, a decline, sometimes precipitous, in the levels of progesterone in maternal plasma normally begins after approximately 95 percent of pregnancy. Moreover, the administration of progesterone to these species late in pregnancy delays the onset of parturition.
In primate pregnancy (including humans), however, progesterone withdrawal does not precede the initiation of parturition. The levels of progesterone in the plasma of pregnant women increase throughout pregnancy, declining only after delivery of the placenta, the tissue site of progesterone synthesis in human pregnancy.
Presently, there appear to be two general theorems. Viewed simplistically, these are the retreat from pregnancy maintenance hypothesis and the uterotonin induction of parturition theory. Several combinations of selected tenets of these two postulates are incorporated into the theorems of most investigators. Some researchers also speculate that the mature human fetus, in some undefined fashion, is the source of the initial signal for the commencement of the parturitional process. This has little direct experimental support in human parturition.
Other investigators suggest that one or another uterotonin, produced in increased amounts or in response to an increase in the population of its myometrial receptors, is the proximate cause of the initiation of human parturition. Indeed, an obligatory role for one or more uterotonins is included in most parturition theories, either as a primary or a secondary phenomenon in the final events of childbirth.
UTERINE PHASES OF PARTURITION
Parturition, the bringing forth of young, encompasses all physiological processes involved in birthing: the prelude to, the preparation for, the process of, and the parturient's recovery from childbirth. From the disparate nature of these physiological processes, it is evident that multiple transformations in uterine function must be accommodated in a timely manner during successful pregnancy and parturition. As shown in Figure 11-15, parturition can be arbitrarily divided into four uterine phases which correspond to the major physiological transitions of the myometrium and cervix during pregnancy (Casey and MacDonald 1993a, 1993c; MacDonald and Casey, 1996).
UTERINE PHASE OF PARTURITION.
Beginning even before implantation, a remarkably effective period of myometrial quiescence is imposed on the uterus. This phase of parturition is characterized by myometrial smooth muscle tranquility with maintenance of cervical structural integrity. This is the phase in which the inherent propensity of the myometrium to contract is harnessed. During this phase, which persists for about the first 95 percent of normal pregnancy, myometrial smooth muscle is rendered unresponsive to natural stimuli and relative contractile paralysis is imposed against a host of mechanical and chemical challenges that otherwise would promote emptying of the uterine contents. The myometrial contractile unresponsiveness of phase 0 is so extraordinary that near the end of pregnancy the myometrium must be awakened from this prolonged parturitional diapause in preparation for labor.
During phase 0 of parturition, as the myometrium is maintained in a quiescent state, the cervix must remain firm and unyielding. The maintenance of cervical anatomical and structural integrity is essential to the success of phase 0 of parturition. Premature cervical dilatation, structural incompetence, or both, portend an unfavorable pregnancy outcome that ends most often in preterm delivery (Chap. 27). Shortening of the cervix, when identified between 24 and 28 weeks of pregnancy, is indicative of increased risk of preterm delivery (Iams and colleagues, 199
UTERINE PHASE 1 OF PARTURITION.
To prepare the uterus for labor, the uterine tranquility of phase 0 of parturition must be suspended; this is the time of uterine awakening. The morphological and functional changes in myometrium and cervix that prepare the uterus for labor may be the natural outcome of the suspension of uterine phase 0; but whatever the mechanism, the capacity of myometrial cells to regulate the concentration of cytoplasmic Ca2+ is restored; myometrial cell responsitivity is reinstituted, uterotonin sensitivity develops, and intercellular communicability is established. As these functional capacities of myometrial smooth muscle to contract are implemented and the cervix is ripened, phase 1 of parturition merges into phase 2, active labor. Challis and Lye (1994) refer to the change in uterine functionality before labor as "activation."
UTERINE MODIFICATION DURING PHASE 1 OF PARTURITION. Specific modifications in uterine function evolve with the suspension of uterine phase 0:
1. A striking increase in myometrial oxytocin receptors.
2. An increase in gap junctions (number and surface area) between myometrial cells.
3. Uterine irritability.
4. Responsiveness to uterotonins.
5. Transition from a contractile state characterized predominantly by occasional painless contractions to one in which more frequent contractions develop.
6. Formation of the lower uterine segment.
7. Cervical softening.
With the development of a well-formed lower uterine segment, the fetal head oftentimes descends to or even through the maternal inlet of the pelvis, a distinctive event referred to as lightening. The abdomen of the pregnant woman commonly undergoes a change in shape, an event sometimes described by the mother as "the baby dropped." No doubt there are many other modifications of the uterus late in pregnancy during phase 1, some of which may be integral components of uterine preparedness for labor.
Late in pregnancy, at sometime during phase 1 of parturition, there is a striking—50-fold or more—increase in the number of oxytocin receptors in myometrium (Fuchs and associates, 1982). This coincides with the increase in uterine contractile responsiveness to oxytocin (Soloff and co-workers, 1979). Also, prolonged human gestation is associated with a delay in this increase in receptors (Fuchs and collaborators, 1984).
Also during phase 1, the number and size of gap junctions between myometrial cells increase before the onset of labor, continue to increase during labor, and then decrease quickly after delivery. This is true of spontaneous parturition, both at term and preterm (Garfield and Hayashi, 1981).
CERVICAL CHANGES OF PHASE 1 OF PARTURITION. The body of the uterus (the fundus) and the cervix, although parts of the same organ, must respond in quite different ways during pregnancy and parturition. On the one hand, it is essential that during most of pregnancy, the myometrium be dilatable but remain quiescent. On the other hand, the cervix must remain unyielding and reasonably rigid. Coincident with the initiation of parturition, however, the cervix must soften, yield, and become more readily dilatable. The fundus must be transformed from the relatively relaxed, unresponsive organ characteristic of most of pregnancy to one that will produce effective contractions that drive the fetus through the yielding (dilatable) cervix and on through the birth canal. Failure of a coordinated interaction between the functions of fundus and cervix portends an unfavorable pregnancy outcome. But despite the apparent reversal of roles between cervix and fundus from before to during labor, it is likely that the processes in both portions of the uterus are regulated by common agents.
COMPOSITION OF THE CERVIX. There are three principal structural components of the cervix: collagen, smooth muscle, and the connective tissue or ground substance. Constituents of the cervix important in cervical modifications at parturition are those in the extracellular matrix and ground substance, the glycosaminoglycans, dermatan sulfate and hyaluronic acid. The smooth muscle content of cervix is much less than that of the fundus, and varies anatomically from 25 to only 6 percent.
CERVICAL SOFTENING. The cervical modifications of phase 1 of parturition principally involve changes that occur in collagen, connective tissue, and its ground substance. Cervical softening is associated with two complementary changes:
1. Collagen breakdown and rearrangement of the collagen fibers.
2. Alterations in the relative amounts of the various glycosaminoglycans.
Hyaluronic acid is associated with the capacity of a tissue to retain water. Near term, there is a striking increase in the relative amount of hyaluronic acid in cervix, with a concomitant decrease in dermatan sulfate. The role for smooth muscle in the cervical softening process is not clear, but may be more important than previously believed. Rath and colleagues (1998) and Winkler and Rath (1999) have addressed this possibility in some detail.
UTERINE PHASE 2 OF PARTURITION. Phase 2 is synonymous with active labor, that is, the uterine contractions that bring about progressive cervical dilatation and delivery of the conceptus. Phase 2 of parturition is customarily divided into the three stages of labor described earlier in the chapter. The onset of labor is the transition from uterine phase 1 to phase 2 of parturition.
UTERINE PHASE 3 OF PARTURITION. Phase 3 encompasses the events of the puerperium—maternal recovery from childbirth, maternal contributions to infant survival, and the restoration of fertility in the parturient. Immediately after delivery of the conceptus, and for about an hour or so thereafter, the myometrium must be held in a state of rigid and persistent contraction/retraction, which effects compression of the large uterine vessels and thrombosis of their lumens. In this coordinated fashion, fatal postpartum hemorrhage is prevented.
During the early puerperium, a maternal-type behavior pattern develops and maternal-infant bonding begins. The onset of lactogenesis and milk let-down in maternal mammary glands also is, in an evolutionary sense, crucial to the bringing forth of young. Finally, involution of the uterus, which restores this organ to the nonpregnant state, and the reinstitution of ovulation must be accomplished in preparation for the next pregnancy. Four to six weeks usually are required for complete uterine involution; but the duration of phase 3 of parturition is dependent on the duration of breast feeding. Infertility usually persists so long as breast feeding is continued because of lactation (prolactin)-induced anovulation and amenorrhea (Chap. 58, p. 1548).
Labor is a physiologic process that permits a series of extensive physiologic changes in the mother to allow for the delivery of her fetus through the birth canal.
It is defined as progressive cervical effacement, dilatation, or both, resulting from regular uterine contractions that occur at least every 5 minutes and last 30-60 seconds.
1. Uterine contractions – is a regular contractions of uterine musculature. Typically, contractions occur every 5 to 10 minutes and last for 20-25 seconds in the onset of labor. As labor proceeds, the contractions become more frequent, more intense, and last longer. In the end of labor the contractions occur every 2-3 minutes and last for 50-to 60 seconds. They are characterized be strength, duration, and frequency which are important in generating a normal labor pattern.
2. Bearing-down efforts (or pushing) – is the periodic contractions of diaphragm, pelvic floor muscles and prelum abdominale which are added to the force of uterine contractions. Its voluntary expulsive force.
There are three stages of labor, each of which is considered separately.
The first stage (cervical) is from the onset of true labor to complete dilatation of the cervix.
The second stage (pelvic) starts from complete dilatation of the cervix to the delivery of the baby.
The third stage (placental) starts from the birth of the baby to delivery of the placenta. It is divided into two phases: placental separation and its expulsion.
During the first stage of the labor cervical effacement and dilatation occur.
Labor begins with cervical effacement ! Cervical effacement is the thinning of the cervix.
Although cervical softening and early effacement may occur before labor, during the first stage of labor the entire cervical length is retracted into lower uterine segment as a result of myometrial contractile forces and pressure exerted by either the presenting part of fetal membranes.
The length of the first stage may vary in relation to parity; primiparous patients generally experience a longer first stage than do multiparous patients. The minimal dilatation during the first stage is for primiparous 1-1,2cm/hour and multiparous women: 1,2-1,5 cm/hour. If the progress is slower than this, evaluation for uterine dysfunction, fetal malposition, or cephalopelvic disproportion should be undertaken.
During the first stage, the progress of labor may be measured in terms of cervical effacement, cervical dilatation and descent of the fetal head. Uterine contractions should be monitored every 30 minutes by palpation for their frequency, duration, and intensity. For high-risk pregnancies, uterine contractions should be monitored continuously along with the fetal heart rate.
Vaginal examination should be done sparingly to decrease the risk of an intrauterine infection. Cervical effacement and dilatation, the station and position of the presenting part, the presence of molding or caput in vertex presentation should be recorded. Additional examinations may be performed if the patient reports the urge to push ( to determine if the full dilatation has occurred) or if a significant fetal heart rate deceleration occurs ( to examine for a prolapsed umbilical cord).
The fetal heart rate should be evaluated by either auscultation with a stethoscope, by external monitoring with Doppler equipment. In patients with no significant obstetric risk factors, the fetal heart rate should be auscultated at least every 30 minutes in the first stage of labor and after each uterine contraction in the second stage of the labor.
At the beginning of the second stage, the mother usually has a desire to bear down with each contraction. This abdominal pressure, together with uterine contractile force, combines to expel the fetus. In cephalic presentation, the shape of the fetal head may be altered during labor, making the assessment of descent more difficult. Molding is the alteration of the relationship of the fetal cranial bones to each other as the result of the compressive forces exerted by the bony maternal pelvis.
The second stage generally takes from 30 minutes to 2 hours in primigravid women and from 10-50 minutes in multigravid women. The median duration is 50 minutes in a primipara and slightly under 20 minutes in a multipara.
Clinical management of the second stage of labor. When delivery is imminent, the patient is usually placed in the lithotomy position.
With each contraction, the mother should be encouraged to hold her breath and bear down with expulsive efforts. As the perineum becomes flattened by the crowning head, an episiotomy may be performed, to prevent perineal lacerations.
As the fetal head crowns (i.e., distends the vaginal opening),
PERINEAL PROTECTIVE MANEUVERS
are performed to avoid injury of the fetus and laceration of the perineum:
The first one is prevention of preterm fetal head extension (during pushing efforts the fetal head is flexed).
Second is the delivery of the fetal head out of the pushing by extension of vulvar muscles.
Third one is decreasing of perineal tension by borrowing of the tissues from the upper part of vulva ring to the lower.
Forth is regulations of voluntary maternal effort (pushing) - woman in labor breaths deeply when the fetus is delivered to the level if parietal tubes. At this moment pushing efforts are contraindicated.
Fifth is the delivery of shoulders – first downward, later upward direction of traction are indicated.
The delivery of the placenta occurs during the third stage of labor. Separation of the placenta generally occurs within 2 to 10 minutes of the end of the second stage of labor. Squeezing of the fundus to hasten placental separation is not recommended because it may increase the likelihood of passage of fetal cells into the maternal circulation.
SIGNS OF PLACENTAL SEPARATION ARE FOLLOWS:
Alfeld’s sign – the umbilical cord lengthens outside the vagina, the clamp, applied on an umbilical cord on the level of pudendal cleft, after placental separation comes down on 10-12 cm.
Shreder’s sign – the uterine fundus rises up, the uterus becomes firm and globular.
Krede-Lasarevich’s sign – a doctor presses with his palm above the patient’s pubis. Before placental separation umbilical cord comes inside a vagina (sign is negative), after separation – comes down (sign is positive).
Only when these signs have appeared the attempt to remove of separated placenta should perform. The placenta should be examined to ensure its complete removal and to detect placental abnormalities. If the patient is at risk of postpartum hemorrhage (e.g., because of anemia, prolonged oxytocic augmentation of labor, multiple gestation or hydroamnions), manual removal of the placenta, manual exploration of the uterus, or both may be necessary. After the placental delivery, the cervix and vagina should be thoroughly inspected for lacerations and surgical repair performed if necessary.
LABOR WITH OCCIPUT PRESENTATIONS
The fetus is in the occiput or vertex presentation in approximately 95 percent of all labors. Presentation is most commonly ascertained by abdominal palpation and confirmed by vaginal examination sometime before or at the onset of labor. In the majority of cases, the vertex enters the pelvis with the sagittal suture in the transverse pelvic diameter (Caldwell and associates, 1934). The fetus enters the pelvis in the left occiput transverse (LOT) position in 40 percent of labors, compared with 20 percent in the right occiput transverse (ROT) position (Caldwell and associates, 1934). In occiput anterior positions (LOA1 or ROA), the head either enters the pelvis with the occiput rotated 45 degrees anteriorly from the transverse position, or subsequently does so. The mechanism of labor usually is very similar to that in occiput transverse positions.
In about 20 percent of labors, the fetus enters the pelvis in an occiput posterior (OP) position. The right occiput posterior (ROP2) is slightly more common than the left (LOP) (Caldwell and associates, 1934). It appears likely from evidence obtained by radiographic studies that posterior positions are more often associated with a narrow forepelvis. They are also more commonly seen in association with anterior placentation (Gardberg and Tuppurainen, 1994a).
OCCIPUT ANTERIOR PRESENTATION
Because of the irregular shape of the pelvic canal and the relatively large dimensions of the mature fetal head, it is evident that not all diameters of the head can necessarily pass through all diameters of the pelvis. It follows that a process of adaptation or accommodation of suitable portions of the head to the various segments of the pelvis is required for vaginal delivery. These positional changes in the presenting part constitute the mechanisms of labor.
ENGAGEMENT. As discussed in Chapter 3 (p. 58), the mechanism by which the biparietal diameter, the greatest transverse diameter of the fetal head in occiput presentations, passes through the pelvic inlet is designated engagement. This phenomenon may take place during the last few weeks of pregnancy, or it may not occur until after the commencement of labor. In many multiparous and some nulliparous women, the fetal head is freely movable above the pelvic inlet at the on-set of labor. In this circumstance, the head is some-times referred to as "floating." A normal-sized head usually does not engage with its sagittal suture directed anteroposteriorly. Instead, the fetal head usually enters the pelvic inlet either in the transverse diameter or in one of the oblique diameters (Caldwell and colleagues, 1934).
Occiput presentations occur in about 95% of all labors. Because of the irregular shape of the pelvic canal and the relatively large dimensions of the mature fetal heard, it is evident that not all diameters of the heard can necessarily pass through all diameters of the pelvis. It follows that a process of adaptation or accommodation of suitable portions of the head to the various segments of the pelvis is required for completion of childbirth.
There are 2 kinds of the occiput presentations – anterior and posterior.
The cardinal movements of labor in anterior occiput presentation are:
· internal rotation;
· internal rotation of the fetal head and external rotation of the fetal body.
The various movements are often described as through they occurred separately and independently. In reality, the mechanism of labor consists of a combination of movements that are going on the same time. For example, as part of process of engagement, there is both flexion and descent of the head. It is manifestly impossible for the movements to be completed unless the presenting part descends simultaneously. The uterine contractions effect important modifications in the attitude, or habitus of the fetus especially after the head has descended into the pelvis. These changes consists principally in a straightening of the fetus, with loss of its dorsal convexity and closer application of the extremities and small parts of the body. As a result, the fetal ovoid is transformed into cylinder with normally the smallest possible cross section passing through the birth canal.
Synclitism and asynclitism. Synclitism is a position when the sagittal suture is in the transverse pelvic diameter. The sagittal suture lie exactly midway between the symphysis and promontory.
If the sagittal suture approaches the sacral promontory, more of the anterior parietal bone presents itself to the examining fingers and the condition is called anterior asynclitism. If the sagittal suture lies close to the symphysis more of the posterior parietal bone presents and the condition is called posterior asynclitism.
The cardinal movements of labor in anterior occiput presentation are:
1. Flexion. As soon as descending head meets resistance, whether from the cervix, the walls of the pelvis, or the pelvic floor, flexion of the head are normally results. In this movement, the chin is brought into more intimate contact with the fetal thorax, and the shorter suboccipitobregmatic diameter is substituted for the longer occipito-frontal diameter. The leader point is the area of the small fontanel.
2. Internal rotation. This movement is a manner that the occiput gradually moves from its original position anteriorly towards the symphysis pubis os. The rotation begins when the fetal head descends from the plane of greatest pelvic dimensions to the least pelvic dimensions (midpelvis). The rotation is complete when the head reaches the pelvic floor, the sagittal suture is in the anteroposterior diameter of the pelvic outlet and the small fontanel is under the symphysis.
3. Extension. After internal rotation the sharply flexed head reaches the pelvic floor, two forces come into play. The first, exerted by the uterus, acts more posteriorly, and the second, supplied by the resistant pelvic floor, acts more anteriorly. The resultant force is the direction of the vulvar opening, thereby causing extension. Extension begins when the fixing point (fossa suboccipitalis) is under the inferior margin of the symphysis pubis. With increasing distension of the perineum and vaginal opening, an increasingly large portion of the occiput gradually appears. The head is born by further extension as the occiput, bregma, forehead, nose, mouse.
4. Internal rotation of the fetal head and external rotation of the fetal body. During the head extension the fetal body is in the pelvic cavity. The biacromial diameter turns from the oblique to the anterioposterior diameter of the pelvic outlet. Thus one shoulder is anterior behind the symphysis and the other is posterior. This movement is brought about apparently by the same pelvic factors that effect internal rotation of the head. The anterior shoulder comes under the symphysis pubis, the fetal body flexed and posterior shoulder is born first. Then the anterior shoulder is born. Fetal head rotates as a result of the body rotation. In the I position fetal face turns towards the right, in the II position towards the left. After delivery of the shoulders, the rest of the body of the child is quickly extruded.
The cardinal movements of labor in posterior occiput presentation are:
1. Flexion. The fetal head flexed and presents the suboccipito-frontal (10 cm) diameter in oblique size of the pelvic inlet. The leader point is a middle part of sagittal suture.
2. Internal rotation. The fetal head passes through the pelvic cavity and in narrow plane it begins rotate. In the outlet plane of pelvis (pelvic floor) the sagittal suture became in the direct (anterioposterior) diameter of the pelvic outlet and the small fontanel is under the sacrum os.
3. Additional flexion. After internal rotation the head reaches the pelvic floor. Fetal head fixes with the area of the border of the hair part of head (the first fixing point) under symphysis pubis and flexes. This process leads to delivery of the vertex.
4. Extension. Extension begins when the second fixing point (fossa suboccipitalis) become under the tip of the sacrum. The head is born by further extension.
5. Internal rotation of the fetal head and external rotation of the fetal body. Shoulder enter to the inlet of small pelvis in oblique size and in pelvic cavity perform the internal rotation to 45 °, in the pelvic floor they stand in the direct (anterioposterior) size. The anterior shoulder comes under the margin of symphysis pubis, the fetal body flexed. The posterior shoulder is born first and then the anterior shoulder is born. The head rotation realize as in anterior occiput presentation.
CHANGES IN SHAPE OF THE FETAL HEAD
In vertex presentations, the fetal head undergoes important characteristic changes in shape as the result of the pressures to which it is subjected during labor. In prolonged labors before complete cervical dilatation, the portion of the fetal scalp immediately over the cervical os becomes edematous, forming a swelling known as the caput succedaneum (Fig. 12-20). It usually attains a thickness of only a few millimeters, but in prolonged labors it may be sufficiently extensive to prevent the differentiation of the various sutures and fontanels. More commonly the caput is formed when the head is in the lower portion of the birth canal and frequently only after the resistance of a rigid vaginal outlet is encountered. Because it occurs over the most dependent area of the head, in LOT3 position it is found over the upper and posterior portion of the right parietal bone, and in ROT positions over the corresponding area of the left parietal bone. It follows that after labor the original position may often be ascertained by noting the location of the caput succedaneum.
Molding describes the change in fetal head shape from external compressive forces. Some molding occurs before labor, possibly related to Braxton Hicks contractions. Although taught in previous editions, most studies indicate that there is seldom overlapping of the parietal bones. Instead, a "locking" mechanism at the coronal and lambdoidal connections prevents such overlapping (Carlan and colleagues, 1991). Molding is associated with a shortened suboccipitobregmatic diameter and a lengthening of the mentovertical diameter. These changes are of greatest importance in contracted pelves or asynclitic presentations. In these circumstances, the degree to which the head is capable of molding may make the difference between spontaneous vaginal delivery versus an operative delivery. Some older literature cited severe head molding as a cause for possible cerebral trauma. Because of the multitude of associated factors, for example, prolonged labor with fetal sepsis and acidosis, it is impossible to quantify the effects of molding with any alleged fetal or neonatal neurological sequelae.
CONDUCT OF NORMAL LABOR AND DELIVERY
The ideal conduct of labor and delivery requires two potentially opposing accommodations on the part of obstetrical providers: first, that birthing be recognized as a normal physiological process that most women experience without complications, and second, that intrapartum complications can arise very quickly and unexpectedly. Thus, providers must simultaneously make the woman and her supporters feel comfortable, yet ensure safety for the mother and infant should complications suddenly develop. The American Academy of Pediatrics and the American College of Obstetricians and Gynecologists (1997) have collaborated in the development of Guidelines for Perinatal Care. These provide detailed information on the appropriate content of intrapartum care to include both personnel and facility requirements..
Pregnant women should be urged to report early in labor rather than to procrastinate until delivery is imminent for fear that they might be experiencing false labor. Early admittance to the labor and delivery unit is important; especially so if during antepartum care the woman, her fetus, or both have been identified as being at risk.
IDENTIFICATION OF LABOR. One of the most critical diagnoses in obstetrics is the accurate diagnosis of labor. If labor is falsely diagnosed, inappropriate interventions to augment labor may be made. Conversely, if labor is not diagnosed, the fetus-infant may be damaged by unexpected complications occurring in sites remote from medical personnel and adequate medical facilities. Although the differential diagnosis between false and true labor is difficult at times, it usually can be made on the basis of the contractions.
Contractions of True Labor
• Contractions occur at regular intervals
• Intervals gradually shorten
• Intensity gradually increases
• Discomfort is in the back and abdomen
• Cervix dilates
• Discomfort is not stopped by sedation
Contractions of False Labor
• Contractions occur at irregular intervals
• Intervals remain long
• Intensity remains unchanged
• Discomfort is chiefly in lower abdomen
• Cervix does not dilate
• Discomfort is usually relieved by sedation
In those instances when a diagnosis of labor cannot be established with certainty, it is often wise to observe the woman over a longer period of time. The general condition of mother and fetus should be ascertained accurately by history and physical examination, including blood pressure, temperature, and pulse. The frequency, duration, and intensity of the uterine contractions should be documented, and the time established when they first become uncomfortable. The degree of discomfort that the mother displays is noted. The heart rate, presentation, and size of the fetus should be determined and documented on admission. The fetal heart rate should be checked, especially at the end of a contraction and immediately thereafter, to identify pathological slowing of the heart rate (Chap. 14, p. 354). Inquiries are made about the status of the fetal membranes and whether there has been any vaginal bleeding. The questions of whether fluid has leaked from the vagina and, if so, how much and when the leakage first commenced are also addressed.
FEDERAL REQUIREMENTS FOR INTER-HOSPITAL TRANSFER OF LABORING WOMEN. All Medicare-participating hospitals with emergency services must provide an appropriate medical screening examination for any pregnant women experiencing contractions who comes to the emergency department for evaluation. The definition of an emergency condition makes specific reference to a pregnant woman who is having contractions. Labor is defined as "...the process of childbirth beginning with the latent phase of labor continuing through delivery of the placenta. A woman experiencing contractions is in true labor unless a physician certifies that after a reasonable time of observation the woman is in false labor." A woman in true labor is considered "unstable" for inter-hospital transfer purposes until the child and placenta are delivered. An unstable woman may, however, be transferred at the direction of the patient or when a physician signs a written certification that benefits of treatment at another facility outweigh the risks of transfer. Physicians and hospitals violating these federal requirements are subject to civil penalties of up to $50,000, as well as termination from the Medicare program.
ELECTRONIC ADMISSION TESTING. Some investigators recommend that a nonstress test (NST) or contraction stress test (CST) be performed on all patients admitted to the labor and delivery unit, the so-called "fetal admission test" (Ingemarsson and associates, 1986). Such fetal surveillance is in reality an assessment of fetal heart rate accelerations or lack of the same with fetal movement (NST1); or an assessment of fetal heart rate before, during, and following a uterine contraction if the patient is in labor (CST2) (Freeman and colleagues, 1991). Fetal heart rate variability and variable decelerations also are used in these evaluations. It has been suggested that such tests of fetal well-being, alone or in combination with fetal acoustic stimulation, will identify unsuspected cases of fetal jeopardy (Ingemarsson and associates, 1988; Sarno and co-workers, 1990). Certainly, if the woman is to be discharged from the labor unit undelivered, this practice is reasonable to ensure, as nearly as possible, that fetal compromise is not identified at this time. At Parkland Hospital, external electronic monitoring is performed for at least one hour before discharging women with false labor.
VAGINAL EXAMINATION. Most often, unless there has been bleeding in excess of bloody show, a vaginal examination under aseptic conditions is performed. Careful attention to the following items is essential in order to obtain the greatest amount of information and to minimize bacterial contamination from multiple examinations.
1. Amnionic fluid. If there is a question of membrane rupture, a sterile speculum is carefully inserted, and fluid is sought in the posterior vaginal fornix. Any fluid is observed for vernix or meconium; if the source of the fluid remains in doubt, it is collected on a swab for further study, as described later.
2. Cervix. Softness, degree of effacement (length), extent of dilatation, and location of the cervix with respect to the presenting part and vagina are ascertained, as will be described. The presence of membranes with or without amnionic fluid below the presenting part often can be felt by careful palpation. The fetal membranes often can be visualized if they are intact and the cervix is dilated somewhat.
3. Presenting part. The nature of the presenting part should be positively determined and, ideally, its position as well, as described in Chapter 12.
4. Station. The degree of descent of the presenting part into the birth canal is identified, as will be described. If the fetal head is high in the pelvis (above the level of the ischial spines), the effect of firm fundal pressure on descent of the fetal head is tested.
5. Pelvic architecture. The diagonal conjugate, ischial spines, pelvic sidewalls, and sacrum are reevaluated for adequacy.
The degree of cervical effacement is usually expressed in terms of the length of the cervical canal compared to that of an uneffaced cervix. When the length of the cervix is reduced by one half, it is 50 percent effaced; when the cervix becomes as thin as the adjacent lower uterine segment, it is completely, or 100 percent, effaced.
This is ascertained by estimating the average diameter of the cervical opening. The examining finger is swept from the margin of the cervix on one side to the opposite side, and the diameter traversed is expressed in centimeters. The cervix is said to be dilated fully when the diameter measures 10 cm, because the presenting part of a term-size infant usually can pass through a cervix this widely dilated.
POSITION OF THE CERVIX.
The relationship of the cervical os to the fetal head is categorized as posterior, midposition, or anterior. A posterior position is suggestive of preterm labor.
The level of the presenting fetal part in the birth canal is described in relationship to the ischial spines, which are halfway between the pelvic inlet and the pelvic outlet. When the lowermost portion of the presenting fetal part is at the level of the ischial spines, it is designated as being at zero (0) station. In the past, the long axis of the birth canal above the ischial spines was arbitrarily divided into thirds. In 1988, the American College of Obstetricians and Gynecologists began using a classification of station that divides the pelvis above and below the spines into fifths. These divisions represent centimeters above and below the spines. Thus, as the presenting fetal part descends from the inlet toward the ischial spines, the designation is -5, -4, -3, -2, -1, then 0 station. Below the ischial spines, the presenting fetal part passes +1, +2, +3, +4, and +5 stations to delivery. Station +5 cm corresponds to the fetal head being visible at the introitus. An approximate correlation of the two methods of describing station is: +2 cm = +1/3 and +4 cm = +2/3 (American Academy of Pediatrics and the American College of Obstetricians and Gynecologists, 1997).
If the leading part of the fetal head is at 0 station or below, most often engagement of the head has occurred; that is, the biparietal plane of the fetal head has passed through the pelvic inlet. If the head is unusually molded, or if there is an extensive caput formation, or both, engagement might not have taken place even though the head appears to be at 0 station.
DETECTION OF RUPTURED MEMBRANES.
The pregnant woman should be instructed during the antepartum period to be aware of leakage of fluid from the vagina and to report such an occurrence promptly. Rupture of the membranes is significant for three reasons. First, if the presenting part is not fixed in the pelvis, the possibility of prolapse of the umbilical cord and cord compression is greatly increased. Second, labor is likely to occur soon if the pregnancy is at or near term. Third, if delivery is delayed for 24 hours or more after membrane rupture, there is increasing likelihood of serious intrauterine infection.
A conclusive diagnosis of rupture of the membranes is made when amnionic fluid is seen pooling in the posterior fornix or clear fluid is passing from the cervical canal (American College of Obstetricians and Gynecologists, 2000). Although several diagnostic tests for the detection of ruptured membranes have been recommended, none is completely reliable. If the diagnosis remains uncertain, another method involves testing the pH of the vaginal fluid; the pH of vaginal secretions normally ranges between 4.5 and 5.5, whereas that of amnionic fluid is usually 7.0 to 7.5. The use of the indicator nitrazine for the diagnosis of ruptured membranes, first suggested by Baptisti (1938), is a simple and fairly reliable method. Test papers are impregnated with the dye, and the color of the reaction is interpreted by comparison with a standard color chart. The pH of the vaginal secretion is estimated by inserting a sterile cotton-tipped applicator deeply into the vagina, and then touching it to a strip of the nitrazine paper and comparing the color of the paper with the chart supplied with the paper. A pH above 6.5 is consistent with ruptured membranes. False-positive tests occur with blood, semen, or bacterial vaginosis and false-negative tests with minimal fluid (American College of Obstetricians and Gynecologists, 2000).
Other tests have been used as markers for rupture of the membranes. Arborization or ferning of vaginal fluid suggests amnionic rather than cervical fluid. Detection of alpha-fetoprotein in the vaginal vault has been used to identify amnionic fluid (Yamada and colleagues, 1998). Unequivocal identification comes from injection of various dyes, including Evans blue, methylene blue, indigo carmine, or fluorescein, into the amnionic sac via abdominal amniocentesis.
VITAL SIGNS AND REVIEW OF PREGNANCY RECORD.
The maternal blood pressure, temperature, pulse, and respiratory rate are checked for any abnormality, and these are recorded. The pregnancy record is promptly reviewed to identify complications. Any problems identified during the antepartum period, as well as any that were anticipated, should be displayed prominently in the pregnancy record.
PREPARATION OF VULVA AND PERINEUM.
The woman is positioned to allow inspection and cleansing of the vulva and perineum. Scrubbing is directed from above, downward, and away from the introitus. Attention should be paid to careful cleansing of the vulvar folds. As the scrub sponge passes over the anal region, it is discarded. If hair on the lower half of the vulva or perineum is felt to interfere at the time of delivery, it can be clipped with scissors or a mini-shave prep can be performed. Routine shaving of the perineum is not performed at Parkland Hospital.
Ideally, after the vulvar and perineal regions have been properly prepared, and the examiner has donned sterile gloves, the thumb and forefinger of one hand are used to separate the labia widely to expose the vaginal opening and prevent the examining fingers from coming in contact with the inner surfaces of the labia. The index and second fingers of the other hand are then introduced into the vagina (Fig. 13-1). A precise routine of evaluation, as described earlier should be followed. It is important to avoid the anal region and not to withdraw the fingers from the vagina until the examination is completed. The number of vaginal examinations during labor does correlate with infectious morbidity, especially in cases of early membrane rupture.
Early in labor, a cleansing enema often is given to minimize subsequent contamination by feces, which otherwise may be a problem during the second stage of labor and delivery. A ready-to-use enema solution of sodium phosphate in a disposable container (Fleet enema) has proven satisfactory. Enemas are not routinely used at Parkland Hospital.
When the woman is admitted in labor, most often the hematocrit, or hemoglobin concentration, should be rechecked. The hematocrit can be measured easily and quickly. Blood may be collected in a plain tube from which a heparinized capillary tube is filled immediately. By employing a small microhematocrit centrifuge in the labor-delivery unit, the value can be obtained in 3 minutes. A labeled tube of blood is allowed to clot and is kept on hand for blood type and screen, if needed, and another is used for routine serology. In some units, a voided urine specimen, as free as possible of debris, is examined for protein and glucose. We obtain a urine specimen for protein analysis only in hypertensive women. Patients who have had no prenatal care should be considered to be at risk for syphilis, hepatitis B, and human immunodeficiency virus (American Academy of Pediatrics and the American College of Obstetricians and Gynecologists, 1997). In unregistered patients, these laboratory studies as well as a blood type, Rh, and antibody screen for atypical antibodies should be performed. Some states, for example Texas, now require routine testing for syphilis, hepatitis B, and human immunodeficiency virus in all women admitted to labor and delivery units.
MANAGEMENT OF FIRST STAGE OF LABOR
As soon as possible after admittance, the remainder of the general physical examination is completed. The physician can best reach a conclusion about the normalcy of the pregnancy when all examinations, including record and laboratory review, are completed. A rational plan for monitoring labor then can be established based on the needs of the fetus and the mother. If no abnormality is identified or suspected, the mother should be reassured. Although the average duration of the first stage of labor in nulliparous women is about 7 hours and in parous women about 4 hours, there are marked individual variations. Any precise statement as to the duration of labor, therefore, is unwise .
MONITORING FETAL WELL-BEING DURING LABOR
It is mandatory for optimal pregnancy outcome that a well-defined program be established that provides careful surveillance of the well-being of both mother and fetus during labor. All observations must be appropriately recorded. The frequency, intensity, and duration of uterine contractions, and the response of the fetal heart rate to the contractions, are of considerable concern. These features can be promptly evaluated in logical sequence.
FETAL HEART RATE.
The fetal heart rate may be identified with a suitable stethoscope or any of a variety of Doppler ultrasonic devices. Changes in the fetal heart rate that most likely are ominous almost always are detectable immediately after a uterine contraction. Therefore, it is imperative that the fetal heart be monitored by auscultation immediately after a contraction. To avoid confusing maternal and fetal heart rates, the maternal pulse should be counted as the fetal heart rate is counted. Otherwise, maternal tachycardia may be misinterpreted as a normal fetal heart rate.
Fetal jeopardy, compromise, or distress—that is, loss of fetal well-being—is suspected if the fetal heart rate immediately after a contraction is repeatedly below 110 bpm. Fetal jeopardy very likely exists if the rate is heard to be less than 100 per minute, even though there is recovery to a rate in the 110 to 160 bpm range before the next contraction. When decelerations of this magnitude are found after a contraction, further labor, if allowed, is best monitored electronically.
The American Academy of Pediatrics and American College of Obstetricians and Gynecologists (1997) recommend that during the first stage of labor, in the absence of any abnormalities, the fetal heart should be checked immediately after a contraction at least every 30 minutes and then every 15 minutes during the second stage. If continuous electronic monitoring is used, the tracing is evaluated at least every 30 minutes during the first stage and at least every 15 minutes during second-stage labor. For women with pregnancies at risk, auscultation is performed at least every 15 minutes during the first stage of labor and every 5 minutes during the second stage. Continuous electronic monitoring may be used with evaluation of the tracing every 15 minutes during the first stage of labor, and every 5 minutes during the second stage.
With the palm of the hand lightly on the uterus, the examiner determines the time of onset of the contraction. The intensity of the contraction is gauged from the degree of firmness the uterus achieves. At the acme of effective contractions, the finger or thumb cannot readily indent the uterus. Next, the time that the contraction disappears is noted. This sequence is repeated in order to evaluate the frequency, duration, and intensity of uterine contractions. It is best to quantify the contractions as regards the degree of firmness or resistance to indentation.
MATERNAL MONITORING AND MANAGEMENT DURING LABOR
MATERNAL VITAL SIGNS. Maternal temperature, pulse, and blood pressure are evaluated at least every 4 hours (Table 13-3). If fetal membranes have been ruptured for many hours before the onset of labor, or if there is a borderline temperature elevation, the temperature is checked hourly. Moreover, with prolonged membrane rupture—defined as greater than 18 hours—antimicrobial administration for prevention of group B streptococcal infections is recommended (American College of Obstetricians and Gynecologists, 1996).
SUBSEQUENT VAGINAL EXAMINATIONS. During the first stage of labor, the need for subsequent vaginal examinations to identify the status of the cervix and the station and position of the presenting part will vary considerably (Table 13-3). When the membranes rupture, an examination should be repeated expeditiously if the fetal head was not definitely engaged at the previous vaginal examination. The fetal heart rate should be checked immediately and during the next uterine contraction in order to detect an occult umbilical cord compression. At Parkland Hospital, periodic pelvic examinations are often performed at 2- to 3-hour intervals to evaluate the progress of labor (Chap. 18, p. 446).
ORAL INTAKE. Food should be withheld during active labor and delivery. Gastric emptying time is remarkably prolonged once labor is established and analgesics are administered. As a consequence, ingested food and most medications remain in the stomach and are not absorbed; instead, they may be vomited and aspirated (Chap. 15, p. 366). There is a trend toward giving liquids in moderation to laboring women (Table 13-3). Guyton and Gibbs (1994) cite studies in which 150 mL of fluids were given orally 2 hours before elective surgery. The incidence of aspiration was not affected. It is unclear whether these studies can be applied to women in labor, who are at risk for urgent cesarean delivery at all times.
INTRAVENOUS FLUIDS. Although it has become customary in many hospitals to establish an intravenous infusion system routinely early in labor, there is seldom any real need for such in the normally pregnant woman at least until analgesia is administered. An intravenous infusion system is advantageous during the immediate puerperium in order to administer oxytocin prophylactically, and at times therapeutically when uterine atony persists. Moreover, with longer labors, the administration of glucose, sodium, and water to the otherwise fasting woman at the rate of 60 to 120 mL/hr is efficacious to prevent dehydration and acidosis
MATERNAL POSITION DURING LABOR. The normal laboring woman need not be confined to bed early in labor. A comfortable chair may be beneficial psychologically and perhaps physiologically. In bed, the laboring woman should be allowed to assume the position she finds most comfortable, which will be lateral recumbency most of the time. She must not be restricted to lying supine. Bloom and colleagues (1998) conducted a randomized trial of walking during labor in over 1000 women with low-risk pregnancies. They found that walking neither enhanced nor impaired active labor and that it was not harmful.
ANALGESIA. Most often, analgesia is initiated on the basis of maternal discomfort. The kinds of analgesia, amounts, and frequency of administration should be based on the need to allay pain on the one hand and the likelihood of delivering a depressed infant on the other.
The timing, method of administration, and size of initial and subsequent doses of systemically acting analgesic agents are based to a considerable degree on the anticipated interval of time until delivery. A repeat vaginal examination is often appropriate before administering more analgesia. With the onset of symptoms characteristic of the second stage of labor, that is, an urge to bear down or "push," the status of the cervix and the presenting part should be reevaluated.
AMNIOTOMY. If the membranes are intact, there is a great temptation even during normal labor to perform amniotomy. The presumed benefits are more rapid labor, earlier detection of instances of meconium staining of amnionic fluid, and the opportunity to apply an electrode to the fetus and insert a pressure catheter into the uterine cavity. The advantages and disadvantages of amniotomy are discussed in Chapter 18 (p. 446). If amniotomy is performed, an aseptic technique should be used. Importantly, the fetal head must be well applied to the cervix and not be dislodged from the pelvis during the procedure; such an action invites prolapse of the umbilical cord.
URINARY BLADDER FUNCTION. Bladder distention should be avoided, because it can lead to obstructed labor and to subsequent bladder hypotonia and infection. During each abdominal examination, the suprapubic region should be visualized and palpated in order to detect a filling bladder. If the bladder is readily seen or palpated above the symphysis, the woman should be encouraged to void. At times she can ambulate with assistance to a toilet and successfully void, even though she could not void on a bedpan. If the bladder is distended and she cannot void, intermittent catheterization is indicated.
MANAGEMENT OF SECOND-STAGE LABOR
With full dilatation of the cervix, which signifies the onset of the second stage of labor, the woman typically begins to bear down, and with descent of the presenting part she develops the urge to defecate. Uterine contractions and the accompanying expulsive forces may last 11/2 minutes and recur at times after a myometrial resting phase of no more than a minute.
The median duration of the second stage is 50 minutes in nulliparas and 20 minutes in multiparas, but it can be highly variable. In a woman of higher parity with a relaxed vagina and perineum, two or three expulsive efforts after the cervix is fully dilated may suffice to complete the delivery of the infant. Conversely, in a woman with a contracted pelvis or a large fetus, or with impaired expulsive efforts from conduction analgesia or intense sedation, the second stage may become abnormally long.
FETAL HEART RATE.
For the low-risk fetus, the heart rate should be auscultated during the second stage of labor at least every 15 minutes, whereas in those at high risk, 5-minute intervals are recommended (American Academy of Pediatrics and the American College of Obstetricians and Gynecologists, 1997). Slowing of the fetal heart rate induced by head compression is common during a contraction and the accompanying maternal expulsive efforts. If recovery of the fetal heart rate is prompt after the contraction and expulsive efforts cease, labor is allowed to continue. Not all instances of fetal heart rate slowing during second-stage labor are the consequence of head compression. The vigorous force generated within the uterus by its contraction and by maternal expulsive efforts may reduce placental perfusion appreciably. Descent of the fetus through the birth canal and the consequent reduction in uterine volume may trigger some degree of premature separation of the placenta, with further compromise of fetal well-being. Descent is more likely to tighten a loop or loops of umbilical cord around the fetus, especially the neck, sufficiently to obstruct umbilical blood flow. Prolonged, uninterrupted maternal expulsive efforts can be dangerous to the fetus in these circumstances. Maternal tachycardia, which is common during the second stage, must not be mistaken for a normal fetal heart rate.
MATERNAL EXPULSIVE EFFORTS.
In most cases, bearing down is reflex and spontaneous during second-stage labor, but occasionally the woman does not employ her expulsive forces to good advantage and coaching is desirable. Her legs should be half-flexed so that she can push with them against the mattress. Instructions should be to take a deep breath as soon as the next uterine contraction begins, and with her breath held, to exert downward pressure exactly as though she were straining at stool. She should not be encouraged to "push" beyond the time of completion of each uterine contraction. Instead, she and her fetus should be allowed to rest and recover from the combined effects of the uterine contraction, breath holding, and considerable physical effort. Gardosi and associates (1989) have recommended a squatting or semi-squatting position using a specialized pillow. They claim that this shortens second-stage labor by increasing expulsive forces and by increasing the diameter of the pelvic outlet. Eason and colleagues (2000) performed an extensive review of positions and their effect on the incidence of perineal trauma. They found that the supported upright position had no advantages over the recumbent one.
Usually, bearing down efforts result in increasing bulging of the perineum—that is, further descent of the fetal head. The woman should be informed of such progress, for encouragement is very important. During this period of active bearing down, the fetal heart rate auscultated immediately after the contraction is likely to be slow, but should recover to normal range before the next expulsive effort.
As the head descends through the pelvis, feces is frequently expelled by the woman. As the head descends still farther, the perineum begins to bulge and the overlying skin becomes tense and glistening. Now the scalp of the fetus may be visible through the vulvar opening (Fig. 13-2). At this time, or before in instances where little perineal resistance to expulsion is anticipated, the woman and her fetus are prepared for delivery.
PREPARATION FOR DELIVERY.
Delivery can be accomplished with the mother in a variety of positions. The most widely used and often the most satisfactory one is the dorsal lithotomy position in order to increase the diameter of the pelvic outlet. In many birthing rooms this is accomplished with the woman lying flat on the bed. For better exposure, leg holders or stirrups are used. In placing the legs in leg holders, care should be taken not to separate the legs too widely or place one leg higher than the other, as this will exert pulling forces on the perineum that might easily result in the extension of a spontaneous tear or an episiotomy into a fourth-degree tear. The popliteal region should rest comfortably in the proximal portion and the heel in the distal portion of the leg-holder. The leg should not be forced to conform to the preexisting setting. The legs are not strapped into the stirrups, thereby allowing quick flexion of the thighs back onto the abdomen should shoulder dystocia be encountered. Cramps in the legs may develop during the second stage in part because of pressure by the fetal head on nerves in the pelvis. Such cramps may be relieved by changing the position of the leg or by brief massage, but leg cramps should never be ignored.
Preparation for delivery entails vulvar and perineal cleansing. If desired, sterile drapes may be placed in such a way that only the immediate area about the vulva is exposed (Fig. 13-3). In the past, the major reason for care in scrubbing, gowning, and gloving was to protect the laboring woman from the introduction of infectious agents. Although these considerations remain valid, concern today also must be extended to the health-care providers, because of the threat of exposure to human immunodeficiency virus. Recommendations for protection of those who care for women during labor and delivery are summarized in Chapter 57 (p. 1498).
DELIVERY OF THE HEAD
With each contraction, the perineum bulges increasingly and the vulvovaginal opening becomes more dilated by the fetal head ), gradually forming an ovoid and finally an almost circular opening. With the cessation of each contraction, the opening becomes smaller as the head recedes. As the head becomes increasingly visible, the vaginal outlet and vulva are stretched further until they ultimately encircle the largest diameter of the fetal head (Fig. 13-5). This encirclement of the largest head diameter by the vulvar ring is known as crowning.
Unless an episiotomy has been made, as described later in the chapter, the perineum by now is extremely thin and, especially in the case of the nulliparous woman, may undergo spontaneous laceration. At the same time, the anus becomes greatly stretched and protuberant, and the anterior wall of the rectum may be easily seen through it. Over many years there has been considerable controversy concerning whether an episiotomy should be cut. We advocate individualization and do not routinely cut an episiotomy. It is now clear that an episiotomy will increase the risk of a tear into the external anal sphincter and/or the rectum. Conversely, anterior tears involving the urethra and labia are much more common in women in whom an episiotomy is not cut.
Immediately after delivery of the infant, there is usually a gush of amnionic fluid, often tinged with blood but not grossly bloody.
CLEARING THE NASOPHARYNX. To minimize the likelihood of aspiration of amnionic fluid, debris, and blood that might occur once the thorax is delivered and the infant can inspire, the face is quickly wiped and the nares and mouth are aspirated.
NUCHAL CORD. Following delivery of the anterior shoulder, the finger should be passed to the neck of the fetus to ascertain whether it is encircled by one or more coils of the umbilical cord (Fig. 13-11). Nuchal cords occur in about 25 percent of cases and ordinarily do no harm. If a coil of umbilical cord is felt, it should be drawn down between the fingers and, if loose enough, slipped over the infant's head. If it is applied too tightly to the neck to be slipped over the head, it should be cut between two clamps and the infant promptly delivered.
CLAMPING THE CORD
The umbilical cord is cut between two clamps placed 4 or 5 cm from the fetal abdomen, and later an umbilical cord clamp is applied 2 or 3 cm from the fetal abdomen. A plastic clamp (Hollister, Double Grip Umbilical Clamp) that is safe, efficient, easy to sterilize, and fairly inexpensive is shown in Figure 13-12.
TIMING OF CORD CLAMPING.
If, after delivery, the infant is placed at or below the level of the vaginal introitus for 3 minutes and the fetoplacental circulation is not immediately occluded by clamping the cord, an average of 80 mL of blood may be shifted from the placenta to the infant (Yao and Lind, 1974). One benefit to be derived from placental transfusion is that the hemoglobin in 80 mL of placental blood that shifts to the fetus eventually provides about 50 mg of iron, which reduces the frequency of iron-deficiency anemia later in infancy. In the presence of accelerated destruction of erythrocytes, as occurs with maternal alloimmunization, the bilirubin formed from the added erythrocytes contributes further to the danger of hyperbilirubinemia (Chap. 39, p. 1061). Although the theoretical risk of circulatory overloading from gross hypervolemia is formidable, especially in preterm and growth-retarded infants, addition of placental blood to the otherwise normal infant's circulation ordinarily does not cause difficulty.
Our policy is to clamp the cord after first thoroughly clearing the airway, all of which usually takes about 30 seconds. The infant is not elevated above the introitus at vaginal delivery or much above the maternal abdominal wall at the time of cesarean delivery.
MANAGEMENT OF THE THIRD STAGE
Immediately after delivery of the infant, the height of the uterine fundus and its consistency are ascertained. As long as the uterus remains firm and there is no unusual bleeding, watchful waiting until the placenta is separated is the usual practice. No massage is practiced; the hand is simply rested on the fundus frequently, to make certain that the organ does not become atonic and filled with blood behind a separated placenta.
SIGNS OF PLACENTAL SEPARATION
Because attempts to express the placenta prior to its separation are futile and possibly dangerous, it is most important that the following signs of placental separation be recognized:
1. The uterus becomes globular and, as a rule, firmer. This sign is the earliest to appear.
2. There is often a sudden gush of blood.
3. The uterus rises in the abdomen because the placenta, having separated, passes down into the lower uterine segment and vagina, where its bulk pushes the uterus upward.
4. The umbilical cord protrudes farther out of the vagina, indicating that the placenta has descended.
These signs sometimes appear within about 1 minute after delivery of the infant and usually within 5 minutes. When the placenta has separated, it should be ascertained that the uterus is firmly contracted. The mother may be asked to bear down, and the intra-abdominal pressure so produced may be adequate to expel the placenta. If these efforts fail, or if spontaneous expulsion is not possible because of anesthesia, and after ensuring that the uterus is contracted firmly, pressure is exerted with the hand on the fundus to propel the detached placenta into the vagina, as depicted and described in Figure 13-13. This approach has been termed physiological management, as later to be contrasted with "active management" of the third stage (Thilaganathan and colleagues, 1993).
DELIVERY OF THE PLACENTA
Placental expression should never be forced before placental separation lest the uterus be turned inside out. Traction on the umbilical cord must not be used to pull the placenta out of the uterus. Inversion of the uterus is one of the grave complications associated with delivery (Chap. 25, p. 642). As pressure is applied to the body of the uterus (Fig. 13-13), the umbilical cord is kept slightly taut. The uterus is lifted cephalad with the abdominal hand. This maneuver is repeated until the placenta reaches the introitus (Prendiville and associates, 1988b). As the placenta passes through the introitus, pressure on the uterus is stopped. The placenta is then gently lifted away from the introitus (Fig. 13-14). Care is taken to prevent the membranes from being torn off and left behind. If the membranes start to tear, they are grasped with a clamp and removed by gentle traction (Fig. 13-15). The maternal surface of the placenta should be examined carefully to ensure that no placental fragments are left in the uterus.
MANUAL REMOVAL OF PLACENTA.
Occasionally, the placenta will not separate promptly. This is especially common in cases of preterm delivery (Dombrowski and colleagues, 1995).. It is unclear as to the length of time that should elapse in the absence of bleeding before the placenta is manually removed. Manual removal of the placenta is rightfully practiced much sooner and more often than in the past. In fact, some obstetricians practice routine manual removal of any placenta that has not separated spontaneously by the time they have completed delivery of the infant and care of the cord in women with conduction analgesia. Proof of the benefits of this practice, however, has not been established, and most obstetricians await spontaneous placental separation unless bleeding is excessive.
ACTIVE MANAGEMENT OF THE THIRD STAGE
Thilaganathan and associates (1993) compared a regimen of active management with syntometrine (5 units of oxytocin with 0.5 mg of ergometrine) and controlled cord traction with one of physiological management wherein the cord was not clamped and the placenta was delivered by maternal efforts. Among 103 low-risk term deliveries, active management resulted in a reduction in the length of the third stage of labor, but no reduction in blood loss compared with physiological management. Mitchell and Elbourne (1993) found that syntometrine administered intramuscularly concurrent with delivery of the anterior shoulder was more effective than oxytocin (5 units intramuscularly) alone in the prevention of postpartum hemorrhage. Duration of the third stage of labor and need for manual removal of the placenta were similar. Side effects of nausea, vomiting, and blood pressure elevations with ergometrine prevented any recommendation for its routine usage.
Puerperium is strictly defined as the period of confinement during and just after birth. By popular use, however, the meaning usually includes the 6 subsequent weeks during which normal pregnancy involution occurs (Hughes, 1972). Of course, and as described in Chapter 8, maternal adaptations to pregnancy do not necessarily all subside completely by 6 weeks postpartum.
CLINICAL AND PHYSIOLOGICAL ASPECTS OF THE PUERPERIUM
The pueperium consists of the period following delivery of the baby and placenta to approximately 6 weeks postpartum. During the puerperium, the reproductive organs and maternal physiology return toward the pregnancy state although menses may not return for much longer.
Involution of the uterus. Immediate after delivery, the fundus of the uterus is easily palpable on the level of the umbilicus. The immediate reduction in uterine size is the result of delivery of the fetus, placenta and amniotic fluid as well as the loss of hormonal stimulation. Further uterine involution is caused by autolysis of intracellular myometrial protein, resulting in a decrease in cell size but not cell number. Through these changes, the uterus returns.
As the myometrial fibers contract, the blood clots from uterus are expelled and the thrombi in the large vessels of the placental bed undergo organization. Within the first 3 days, the remaining decidua differentiates into a superficial layer, which becomes necrotic and sloughs, and a basal layer adjacent to the myometrium, which contained the fundi of the endometrial glands and is the source of the new endometrium.
Immediately after the delivery of the placenta, the uterus is palpated bimanually to ascertain that it is firm.
This discharge is fairly heavy at first and rapidly decreases in amount over the first 2 to 3 days postpartum, although it may last for several weeks.
1-3 day after labor – bloody
4-6 day after labor – bloody-serous
7-9 day after labor – serous-bloody
10 day after labor – serous
For the first few days after delivery, the uterine discharge appears red ( lochia rubra) owing the presents of erythrocytes. After 3 to 4 days, the lochia becomes paler ( lochia serosa), and by the tenth day, it assumes a white or yellow- white color ( lochia alba). By the end of the third week postpartum, the endometrium is reestablished in most patients.
Cervix. Just after the labor the cervix admits the hand. Within several hours of delivery the cervix has reformed, and on 4-5 day it usually admits only one finger (i.e., it is approximately 1cm in diameter), on 9-10 day cervix closed. The round shape of the nulliparous cervix is usually permanently replaced by a transverse, fish-mouth shaped external os, the result of laceration during delivery. Vulvar and vaginal tissues return to normal over the first several days, although the vaginal mucosa reflects a hypoestrogenic state if the woman breast-feeds because ovarian function is suppressed during breast-feeding.
Abdominal wall. Return of the elastic fibers of the stretched rectus muscles to normal configuration occurs slowly and is aided by exercise.
At time of delivery, the drop of estrogen and other placental hormones is a major factor in removing the inhibition of the action of prolactin. also, suckling by the infant stimulates release of oxytocin from the neurohypophysis. On approximately the second day after delivery, colostrum is secreted. After about 3 to 6 days, the colostrum is replaced by mature milk.
CHANGES IN THE CERVIX AND LOWER UTERINE SEGMENT.
The outer cervical margin, which corresponds to the external os, is usually lacerated, especially laterally. The cervical opening contracts slowly, and for a few days immediately after labor it readily admits two fingers. By the end of the first week, it has narrowed. As the opening narrows, the cervix thickens, and a canal reforms. At the completion of involution, however, the external os does not resume its pregravid appearance completely. It remains somewhat wider, and typically, bilateral depressions at the site of lacerations remain as permanent changes that characterize the parous cervix. It should also be kept in mind that the cervical epithelium undergoes considerable remodeling as a result of childbirth. For example, Ahdoot and colleagues (1998) found that approximately 50 percent of women with high-grade squamous intraepithelial cells showed regression as a result of vaginal delivery.
The markedly thinned-out lower uterine segment contracts and retracts but not as forcefully as the body of the uterus. Over the course of a few weeks, the lower segment is converted from a clearly evident structure, large enough to contain most of the fetal head, into a barely discernible uterine isthmus located between the uterine corpus above and the internal cervical os below .
INVOLUTION OF THE UTERINE CORPUS.
Immediately after placental expulsion, the fundus of the contracted uterus is slightly below the umbilicus. The uterine body then consists mostly of myometrium covered by serosa and lined by basal decidua. The anterior and posterior walls, in close apposition, each measure 4 to 5 cm in thickness. Because its vessels are compressed by the contracted myometrium, the puerperal uterus on section appears ischemic when compared with the reddish-purple hyperemic pregnant organ. After the first 2 days, the uterus begins to shrink, so that within 2 weeks it has descended into the cavity of the true pelvis. It regains its previous nonpregnant size within about 4 weeks. The immediately postpartum uterus weighs approximately 1000 g. As the consequence of involution, 1 week later it weighs about 500 g, decreasing at the end of the second week to about 300 g, and soon thereafter to 100 g or less. The total number of muscle cells does not decrease appreciably; instead, the individual cells decrease markedly in size. The involution of the connective tissue framework occurs equally rapidly.
Because separation of the placenta and membranes involves the spongy layer, the decidua basalis remains in the uterus. The decidua that remains has striking variations in thickness, an irregular jagged appearance, and is infiltrated with blood, especially at the placental site.
AFTERPAINS. In primiparas the puerperal uterus tends to remain tonically contracted. Particularly in multiparas, the uterus often contracts vigorously at intervals, giving rise to afterpains. Occasionally these pains are severe enough to require an analgesic. Afterpains are noticeable particularly when the infant suckles, likely because of oxytocin release. Usually, they decrease in intensity and become mild by the third postpartum day.
Conventional obstetrical wisdom has for many years taught that lochia lasted for approximately 2 weeks after delivery. Recent studies, however, have indicated that lochia persists for up to 4 weeks and may stop and resume up to 56 days after delivery (Oppenheimer and colleagues, 1986; Visness and co-workers, 1997). Maternal age, parity, infant weight, and breast feeding do not influence the duration of lochia.
In some centers, it is routine to prescribe an oxytocic agent to hasten uterine involution by promoting uterine contractility. This also presumably diminishes bleeding complications. Newton and Bradford (1961), however, concluded that after the period immediately following delivery, routine administration of intramuscular oxytocin to normal women was of no value in decreasing blood loss or hastening uterine involution.
Within 2 or 3 days after delivery, the remaining decidua becomes differentiated into two layers. The superficial layer becomes necrotic, and it is sloughed in the lochia. The basal layer adjacent to the myometrium remains intact and is the source of new endometrium. The endometrium arises from proliferation of the endometrial glandular remnants and the stroma of the interglandular connective tissue.
Endometrial regeneration is rapid, except at the placental site. Within a week or so, the free surface becomes covered by epithelium, and the entire endometrium is restored during the third week. Sharman (1953) identified fully restored endometrium in all biopsy specimens obtained from the 16th postpartum day onward. So-called endometritis identified histologically during the puerperium is only part of the normal reparative process. Similarly, in almost half of postpartum women, fallopian tubes, between 5 and 15 days, demonstrate microscopical inflammatory changes characteristic of acute salpingitis. This, however, is not infection, but only part of the involutional process (Andrews, 1951).
SUBINVOLUTION. This term describes an arrest or re-tardation of involution, the process by which the puerperal uterus is normally restored to its original proportions. It is accompanied by prolongation of lochial discharge and irregular or excessive uterine bleeding and sometimes by profuse hemorrhage. On bimanual examination, the uterus is larger and softer than normal for the particular period of the puerperium. Among the recognized causes of subinvolution are retention of placental fragments and pelvic infection. Because most cases of subinvolution result from local causes, they are usually amenable to early diagnosis and treatment. Ergonovine (Ergotrate) or methylergonovine (Methergine), 0.2 mg every 3 to 4 hours for 24 to 48 hours, is recommended by some clinicians, but its efficacy is questionable. On the other hand, metritis responds to oral antimicrobial therapy. Wager and colleagues (1980) reported that almost a third of cases of later postpartum uterine infection are caused by Chlamydia trachomatis; thus tetracycline therapy may be appropriate.
Andrew and colleagues (1989) described 25 cases of hemorrhage between 7 and 40 days postpartum associated with noninvoluted uteroplacental arteries. These abnormal arteries were characterized by no detectable endothelial lining and the vessels were filled with thrombi. Periauricular trophoblasts were also present in the walls of these vessels and the authors postulated that subinvolution, at least with regard to the placental vessels, may represent an aberrant interaction between uterine cells and trophoblast.
PLACENTAL SITE INVOLUTION. According to Williams (1931), complete extrusion of the placental site takes up to 6 weeks. This process is of great clinical importance, for when it is defective, late-onset puerperal hemorrhage may ensue. Immediately after delivery, the placental site is about the size of the palm of the hand, but it rapidly decreases thereafter. By the end of the second week, it is 3 to 4 cm in diameter. Within hours of delivery, the placental site normally consists of many thrombosed vessels that ultimately undergo the typical organization of a thrombus.
Williams (1931) explained involution of the placental site as follows:
Involution is not effected by absorption in situ, but rather by a process of exfoliation which is in great part brought about by the undermining of the implantation site by growth of endometrial tissue. This is affected partly by extension and downgrowth of endometrium from the margins of the placental site and partly by the development of endometrial tissue from the glands and stroma left in the depths of the decidua basalis after placental separation. Such exfoliation should be regarded as very conservative, and as a wise provision; otherwise great difficulty might be experienced in sloughing obliterated arteries and organized thrombi which, if they remained in situ, would soon convert a considerable part of the uterine mucosa and subjacent myometrium into a mass of scar tissue.
Anderson and Davis (1968) concluded that placental site exfoliation is brought about as the consequence of sloughing of infarcted and necrotic superficial tissues followed by a reparative process.
Anlagen of mammary glands are contained in ectodermal ridges that form on the ventral surface of the embryo and extend laterally from forelimb to hindlimb. The multiple pairs of buds normally disappear from the embryo except for one pair in the pectoral region that eventually develops into the two mammary glands . At times, however, the buds elsewhere may not completely disappear, but instead they may participate to an amazing degree in the pattern of growth that characterizes the two normal mammary glands.
At midpregnancy, each of the two fetal mammary buds destined to form the breasts begins to grow and divide. This results in the formation of 15 to 25 secondary buds that provide the basis for the duct system in the mature breast. Each secondary bud elongates into a cord, bifurcates, and differentiates into two concentric layers of cuboidal cells and a central lumen. The inner layer of cells eventually gives rise to the secretory epithelium, which synthesizes the milk. The outer cell layer becomes myoepithelium, which provides the mechanism for milk ejection .
Thelarche is the onset of rapid breast growth that begins about the time of puberty when estrogen production rises. The previously infantile mammary glands respond to estrogen with growth and development of mammary ducts and fat deposition. With ovulation, progesterone stimulates development of the alveoli for future lactation.
Anatomically, each mature mammary gland is composed of 15 to 25 lobes that arose from the secondary buds described previously. The lobes are arranged radially and are separated from one another by varying amounts of fat. Each lobe consists of several lobules, which in turn are made up of large numbers of alveoli Every alveolus is provided with a small duct that joins others to form a single larger duct for each lobe. These lactiferous ducts open separately upon the nipple, where they may be distinguished as minute but distinct orifices. The alveolar secretory epithelium synthesizes the various milk constituents.
LACTATION. Colostrum is the deep lemon-yellow colored liquid secreted initially by the breasts. It usually can be expressed from the nipples by the second postpartum day.
Compared with mature milk, colostrum contains more minerals and protein, much of which is globulin, but less sugar and fat. Colostrum nevertheless contains large fat globules in so-called colostrum corpuscles. These are thought by some investigators to be epithelial cells that have undergone fatty degeneration and by others to be mononuclear phagocytes containing fat. Colostrum secretion persists for about 5 days, with gradual conversion to mature milk during the ensuing 4 weeks. Antibodies are demonstrable in the colostrum, and its content of immunoglobulin A may offer protection for the newborn against enteric pathogens. Other host resistance factors, as well as immunoglobulins, are found in human colostrum and milk. These include complement, macrophages, lymphocytes, lactoferrin, lacto-peroxidase, and lysozymes.
Human milk is a suspension of fat and protein in a carbohydrate-mineral solution. A nursing mother easily makes 600 mL of milk per day. Milk is isotonic with plasma, with lactose accounting for half of the osmotic pressure. Major proteins, including a-lactalbumin, ß-lactoglobulin, and casein, are also present. Essential amino acids are derived from blood, and nonessential amino acids are derived in part from blood or synthesized in the mammary gland. Most milk proteins are unique and not found elsewhere. Whey has been shown to contain large amounts of interleukin-6 (Saito and co-workers, 1991). Peak levels of this cytokine were found in colostrum, and there was a positive correlation between its concentration and the number of mononuclear cells in human milk. Additionally, interleukin-6 was associated closely with local immunoglobulin A production by the breast. Prolactin appears to be actively secreted into breast milk (Yuen, 1988). Epidermal growth factor (EGF) has also been identified in human milk (Koldovsky and associates, 1991; McCleary, 1991). Because this factor is not destroyed by gastric proteolytic enzymes, it may be absorbed orally and promote growth and maturation of intestinal mucosa.
There are major changes in milk composition by 30 to 40 hours postpartum, including a sudden increase of lactose concentration. Lactose synthesis from glucose in alveolar secretory cells is catalyzed by lactose synthase (Fig. 17-4). Some lactose enters the maternal circulation and is excreted by the kidney. This may be misinterpreted as glucosuria unless specific glucose oxidase is used in testing. Fatty acids are synthesized in the alveoli from glucose and are secreted by an apocrine-like process.
All vitamins except vitamin K are found in human milk, but in variable amounts, and maternal dietary supplementation increases the secretion of most of these (American Academy of Pediatrics, 1981). Vitamin K administration to the infant soon after delivery is required to prevent hemorrhagic disease of the newborn.
Human milk contains a low iron concentration and maternal iron stores do not seem to influence the amount of iron in breast milk. Therefore, the use of supplemental iron-fortified infant formulas, or a weaning formula also fortified with iron, is recommended (American Academy of Pediatrics, 1997). Such formulas apparently have eliminated iron-deficiency anemia during childhood (Yip and associates, 1987). These formulas are well tolerated by most infants and there is no evidence that they impair absorption of zinc or copper (Nelson and associates, 1988; Yip and colleagues, 1985).
Mennella and Beauchamp (1991) documented what experienced nursing mothers have long known: breast-fed infants are aware of what their mothers eat and drink. They studied the effects of maternal ethanol ingestion equivalence to one can of beer. This caused the infants to suck more frequently during the first minute of feeding, but ultimately they consumed significantly less milk.
The mammary gland, like the thyroid gland, concentrates iodine and several other minerals, including gallium, technetium, indium, and possibly sodium. Radioactive isotopes of these minerals should not be given to nursing women because they rapidly appear in breast milk. The American Academy of Pediatrics (1997) recommends consultation with a nuclear medicine physician before performing a diagnostic study, so that a radionuclide with the shortest excretion time in breast milk can be used. They further recommend that the mother pump her breasts before the study and store enough milk in a freezer for feeding the infant. After the study, she should pump her breasts to maintain milk production, but discard all milk produced during the time that radioactivity is present. This ranges from 15 hours up to 2 weeks, depending upon the isotope used.
The approximate concentrations of the more important components of human colostrum, mature human milk, and cow milk are presented in Table 17-1. These concentrations vary depending upon maternal diet and when studied in the puerperium (Brasil and co-workers, 1991; Giovannini and colleagues, 1991; Ogunleye and associates, 1991). Gestational weight gain has little, if any, impact on the subsequent milk quantity or quality (Institute of Medicine, 1990).
ENDOCRINOLOGY OF LACTATION.
The precise humoral and neural mechanisms involved in lactation are complex. Progesterone, estrogen, and placental lactogen, as well as prolactin, cortisol, and insulin, appear to act in concert to stimulate the growth and development of the milk-secreting apparatus of the mammary gland (Porter, 1974). With delivery, there is an abrupt and profound decrease in the levels of progesterone and estrogen, which removes the inhibitory influence of progesterone on the production of a-lactalbumin by the rough endoplasmic reticulum . The increased a-lactalbumin serves to stimulate lactose synthase and ultimately increased milk lactose. Progesterone withdrawal also allows prolactin to act unopposed in its stimulation of a-lactalbumin production.
The intensity and duration of subsequent lactation are controlled, in large part, by the repetitive stimulus of nursing. Prolactin is essential for lactation; women with extensive pituitary necrosis, as in Sheehan syndrome, do not lactate. Although plasma prolactin falls after delivery to lower levels than during pregnancy, each act of suckling triggers a rise in levels (McNeilly and associates, 1983). Presumably a stimulus from the breast curtails the release of prolactin-inhibiting factor from the hypothalamus; this, in turn, transiently induces increased prolactin secretion.
The neurohypophysis, in pulsatile fashion, secretes oxytocin. This stimulates milk expression from a lactating breast by causing contraction of myoepithelial cells in the alveoli and small milk ducts. Milk ejection, or "letting down," is a reflex initiated especially by suckling, which stimulates the neurohypophysis to liberate oxytocin (McNeilly and associates, 1983). It may be provoked even by the cry of the infant or inhibited by fright or stress.
In women who continue lactating but who resume ovulation, there are acute alterations in breast milk composition 5 to 6 days before and 6 to 7 days following ovulation (Hartmann and Prosser, 1984). These changes are abrupt and characterized by increased concentrations of sodium and chloride, along with decreased potassium, lactose, and glucose concentrations. In women who become pregnant but who continue to breast feed, milk composition undergoes progressive alterations suggesting gradual loss of metabolic and secretory breast activity
Nipple care is also important during breast-feeding. The nipples should be washed with water and exposed to the air for 15 to 20 minutes after each feeding. A water-based cream such as lanolin or vitamin A and D ointment may be applied if the nipples are tender.
Mastitis is an uncommon complication of breast-feeding and usually develops 2 to 4 weeks after beginning breast-feeding. The first symptoms are usually slight fever and chills. These are followed by redness of a segment of the breast, which becomes indurated and painful. The etiologic agent is usually Staphylococcus aureus, which originates from the infant’s oral pharynx. Milk should be obtained from the breast for the culture and sensitivity, and mother should be started on a regimen of antibiotics immediately. Because the majority of staphylococcal organisms are penicillinase-producing, a penicillinase-resistant antibiotic, such as dicloxacillin, should be used. Breast-feeding should be discontinued, and an appropriate antibiotic should be continued for 7 to 10 days. If a breast abscess ensues, it should be surgically drained. A breast pump can be used to maintain lactation until the infection has cleared, but the milk should be discarded. The infant, along with other family members, should be evaluated for staphylococcal infections that may be source of reinfection if breast-feeding is resumed.