Physiology of Delivery

Physiology of Delivery. Analgesia in labor

                                                                 Prepared by Korda I.

Attitude:  This refers to the posturing of the joints and relation of fetal parts to one another. The normal fetal attitude when labor begins is with all joints in flexion.

Lie:  This refers to the longitudinal axis of the fetus in relation to the mother's longitudinal axis (i.e., transverse, oblique, or longitudinal (parallel).

Presentations:   This describes the part on the fetus lying over the inlet of the pelvic or at the cervical os.

Point of Reference of Direction:  This is an arbitrary point on the presenting part used to orient it to the maternal pelvis [usually occiput, mentum (chin) or sacrum].

Position:   This describes the relation of the point of reference to one of the eight octanes of the pelvic inlet (e.g., LOT: the occiput is transverse and to the left).

Engagement:  This occurs when the biparietal diameter is at or below the inlet of the true pelvis.

Station:   This references the presenting part to the level of the ischial spines measured in plus or minus centimeters.

Flexion and Engagement:   This occurs at various times before the forces of labor begin.

Descent:   This occurs as a result of active forces of labor.

Internal Rotation:   This occurs as a result of impingement of the presenting part on the bony and soft tissues of the pelvis.

Extension:  This is the mechanism by which the head normally negotiates the pelvic curve.

External Rotation(Restitution):   This is the spontaneous realignment of the head with the shoulders.

Expulsion:   This is anterior and the posterior shoulders, followed by trunk and lower extremities in rapid succession.

History: A complete medical history should be obtained, including medical conditions; medication use (prescription, over-the-counter, supplements); diet; use of alcohol, tobacco, and illicit drugs; both family and menstrual history (age of menarche, usual menstrual pattern, date of onset of last menses, contraceptive use, history of irregular menses); and history of previous pregnancies. Many women miss a menstrual period before they suspect pregnancy. Early symptoms may include tender, swollen breasts, nausea, vomiting, frequent urination, and fatigue.

Physical exam: The exam may reveal enlargement of the uterus on bimanual examination, softening of the uterus and cervix (Hegar’s sign) at 6 weeks, bluish color of the vagina (Chadwick’s sign) at 8 to 10 weeks, and enlargement of the breasts. At 10 to 12 weeks, fetal heart tones can be heard through a special stethoscope. The uterus may be palpable low in the abdomen by 12 weeks.

Tests: Pregnancy can be confirmed through laboratory tests or home test kits that check for hCG in serum or urine. Over-the-counter or home pregnancy test kits can detect hCG in urine and become positive 9 to 12 days after conception. hCG can be detected in the serum in 5% of pregnant women 5 days after conception and in over 98% of pregnant women by 11 days after conception. Serum hCG tests have a low false positive rate of 0.01% to 2%. A false positive test is caused by substances in the woman’s body such as antibodies, rheumatoid factor, or proteins that interfere with the test. False negative tests usually occur with urine samples and usually are due to interference from medications, dilute urine samples, or errors in following testing directions.

 Other initial testing may be done to screen for conditions that may affect the health of the mother and fetus. Urinalysis screens for urinary tract infections and kidney problems. Complete blood count (CBC) tests for anemia, infection, and other blood problems. Antibody testing looks for syphilis and rubella (German measles) antibodies and blood group and Rh typing identifies blood group antigens. Individuals at risk for diabetes receive a glucose tolerance test. Additional tests may be done to screen for hepatitis B, toxoplasmosis, and HIV. Cervical cultures may be done to rule out infection.

Ultrasound reveals the age of the fetus, presence of multiple fetuses, abnormal physical development of the fetus, and location of the placenta. Ultrasound carries no known risk to the woman or her fetus. Few studies have been able to prove that ultrasound is absolutely necessary, but it has produced two positive results: fewer pregnancies go past their due dates, and women carrying fetuses with anomalies can make decisions about termination earlier in the pregnancy. Ultrasound can be done at any time, but it is most useful during the second trimester between weeks 18 and 20; a second ultrasound can be done at 23 to 28 weeks.

 Prenatal diagnosis of congenital malformations and genetic disorders has increased with the development of accurate testing methods. Testing is often recommended for women who: 1) are age 35 or older; 2) have a history of parental consanguinity; 3) have a personal or parental history of a child with a chromosomal abnormality (e.g., Down syndrome, male relatives with Duchenne muscular dystrophy, severe hemophilia); 4) have experienced recurrent miscarriages; 5) has type 1 diabetes mellitus, epilepsy, or myotonic dystrophy; 6) has been exposed to certain medications, environmental hazards, or viral infections (e.g., rubella, cytomegalovirus).

 Measurement of alpha-fetoprotein (AFP) levels in maternal blood serum screens for neural tube defects such as absence of all or part of the brain (anencephaly) and protrusion of part of the spinal cord through a gap in the spinal column which usually results in loss of voluntary movement in the lower body (spina bifida). AFP is a protein made by the fetus’s liver. If the fetus's spinal cord has not developed correctly, increased amounts of AFP may leak into the mother's bloodstream. Elevated levels of AFP in the maternal bloodstream can also occur with gestational diabetes, twins, intrauterine growth retardation, increased gestational age, and in pregnancies complicated by bleeding. Low levels of AFP in the mother’s bloodstream may suggest the presence of chromosomal abnormalities such as Down syndrome. Testing is most sensitive at a gestational age of 16 to18 weeks but can be performed anywhere between 15 and 22 weeks of gestation. At 15 to 20 weeks, maternal serum levels of AFP, hCG, and estriol can be measured. Each of these substances is a marker for potential fetal abnormalities. Checking the levels of these markers simultaneously increases screening sensitivity.

 Analysis of the amniotic fluid (amniocentesis) that surrounds the developing fetus, is used to detect fetal genetic abnormalities in pregnant women over age 35 or in those whose family history puts them at high risk for certain genetic defects. It is usually performed between weeks 14 and 20 of the pregnancy. Under ultrasound guidance, a long needle is passed through the mother’s lower abdomen into the uterus, and a small amount of fluid is withdrawn. The fetal cells that have been shed into the fluid are analyzed for chromosomal problems (e.g., Down syndrome), and the fluid is analyzed for abnormally high level of AFP. Later in the pregnancy the test can determine the maturity of the fetus's lungs or if there is Rh incompatibility between fetus and mother. The procedure carries an increased risk of miscarriage and maternal Rh sensitization.

 Chorionic villus sampling is another form of invasive testing for chromosomal abnormalities and genetic defects. Small pieces of the placenta are removed through a catheter inserted into the uterus under ultrasound guidance. The primary advantage of chorionic villus sampling is that the procedure can be performed at 10 to 12 weeks gestation, whereas amniocentesis is performed at 14 to 20 weeks gestation. The risk of miscarriage with chorionic villus sampling is 2% to 3% higher than for amniocentesis. There is also a small risk of injury to the developing fetus’ limbs.


 Percutaneous umbilical cord sampling is used after 16 weeks gestation for rapid chromosome analysis as well as evaluation of fetal metabolism and fetal blood abnormalities. Guided by images on ultrasound, a doctor inserts a needle into the mother’s abdomen and withdraws a sample of the baby’s blood from the umbilical cord. Because this is an invasive procedure, percutaneous umbilical cord sampling carries risks for both mother and fetus.

 If the mother is of African origin, a test for sickle cell anemia may be ordered. Jewish mothers of eastern European ancestry (Ashkenazi Jews) and French Canadians should be tested for the Tay-Sachs gene.


Regular prenatal visits to a physician or maternity clinic are essential for a healthy, safe pregnancy, delivery, and postpartum recovery.


 For an uncomplicated pregnancy, visits usually are scheduled every 4 weeks during the first and second trimester and every 2 weeks during the third trimester. At week 36, visits are increased to weekly until delivery. A mother who goes past her due date may be seen 2 to 3 times a week.

 At each prenatal visit, blood pressure, weight, fundal height, and fetal heart rate are measured and recorded. Urine is tested for abnormal amounts of glucose and albumin (urinalysis).

 Each mother should receive information regarding proper nutrition, exercise, sexual activity, work activity, tobacco and alcohol use, and medication restrictions. Prenatal vitamins usually are prescribed. Childbirth classes, breastfeeding instruction, and family planning should be offered.



Most individuals will deliver a healthy child and have a complete, uncomplicated recovery.



Rehabilitation for normal pregnancy can be re-cast in terms of working during pregnancy. Most women can continue to work in jobs to which they are acclimated during most of pregnancy (Gabbe).


 While exposure to toxic substances that might harm the fetus should logically be avoided, no one has published a list of occupations or jobs that should be avoided by pregnant women based on known exposures.

 Exercise during pregnancy is to some degree analogous to the physical demands of work during pregnancy. Exercise in general in healthy women with normal pregnancies is strongly recommended. Both the American College of Obstetricians and Gynecologists and the Society of Obstetricians and Gynaecologists of Canada have published guidelines that strongly recommend routine exercise during pregnancy.

 These guidelines state that exercise has been shown to have beneficial effects on maternal health and pregnancy outcome. Theoretical concerns--about pregnant women being at increased risks of fall due to their altered centers of gravity, and being at increased risk of sprains and strains due to hormonally mediated increased ligamentous laxity--have not been substantiated by data.

 Although exercise during pregnancy usually is safe, several things should be avoided. A pregnant woman should avoid holding her breath during exercise (Valsalva maneuver) because this restricts oxygen flow to the placenta. Exercising while lying on the back (supine position) after the first trimester is not recommended because this decreases the cardiac output to the fetus. Activities such as skiing or horseback riding, in which falls could harm the mother or fetus, should be avoided.

 In any workout, the woman should pay special attention to strengthening the lower back and pelvic floor muscles (Kegel exercises). In addition to strength training, a cardiovascular workout of walking or riding a bicycle is recommended. If a specific exercise causes pain or discomfort, it should be discontinued and an alternative exercise initiated. According to the American College of Obstetricians and Gynecologists (ACOG), exertion during pregnancy should be governed by the woman’s own good judgment--she can push herself as much or as little as she is comfortable.

 Both guidelines contain absolute and relative contraindications to exercise during pregnancy, and logically these conditions would be potential contraindications to moderate, heavy, or very heavy work.

 Absolute Contraindications to Exercise During Pregnancy:

 - Uncontrolled type 1 diabetes, thyroid disease, or other serious cardiovascular, respiratory, or systemic disorder

 - Growth restricted fetus

 - Incompetent cervix/cerclage (prior miscarriages)

 - Multiple gestation at risk for premature labor

 - Persistent second or third trimester bleeding

 - Placenta previa after 26 weeks gestation

 - Premature labor during the current pregnancy

 - Ruptured membranes

 - Pregnancy induced hypertension

 - Preeclampsia


 Relative Contraindications to Exercise During Pregnancy:

 - Severe anemia (Hemoglobin < 100 gm/L)

 - Unevaluated maternal cardiac arrhythmia

 - Mild/moderate cardiovascular or respiratory disorder

 - Chronic bronchitis

 - Poorly controlled type I diabetes

 - Extreme morbid obesity

 - Extreme underweight (body mass index <12), malnutrition or eating disorder

 - History of extremely sedentary lifestyle

 - Intrauterine growth restriction in current pregnancy

 - Poorly controlled hypertension/preeclampsia

 - Orthopaedic limitations

 - Poorly controlled seizure disorder

 - Poorly controlled thyroid disease

 - Heavy smoker


 The concerns with work and pregnancy relate to hypertension/preeclampsia, premature delivery, and delivery of small--for gestational age--children (intrauterine growth retardation). In recent years, more women are working during pregnancy, and more women are working to within 1 month of delivery.

 In the meta-analysis of 29 published studies (Mozurkewich), statistically significant but very minor risks were found for some work activities and pregnancy outcome. Mozurkewich estimates that one preterm birth might be prevented for each . . .

 - 27 to 80 women who discontinue prolonged standing;

 - 23 to 171 women who discontinue shift or night work;

 - 36 to 65 women who discontinue physically demanding work;

 - 12 to 32 women who modify cumulative work fatigue factors.

 Thus, based on this meta-analysis, work would be safe for most pregnant women, but work restrictions could be imposed by the woman’s physician if there were any indication of any complications occurring during the monitoring of pregnancy.

 A systematic review by Bonzini (2007) found 53 studies on work and/or physical activity on preterm delivery, 34 studies on low birth weight, and 9 on preeclampsia. For pre-term delivery and small for gestational age the larger and more complete studies were less positive and risk was only modest or not present. This review concluded there was not significant evidence to justify mandatory activity or work restrictions.

 In summary, work during pregnancy is usually a question of whether a woman can safely continue to work at a job to which she is accustomed. The risk of continuing to work is small, and most of the conditions that might be caused by continuing to work can be monitored by the woman’s physician. If any of the absolute or relative contraindications to exercise during pregnancy are present or develop, the pregnant woman’s physician will logically impose work restrictions.

 In the absence of these problems, during an uncomplicated normal pregnancy, the following durations mark the time at which the pregnant woman should stop that type of work activity:

 Sedentary - at onset of labor or 40 weeks gestation

 Light - at 38 weeks gestation

 Moderate - at 32 weeks gestation

 Heavy - at 26 weeks gestation

 Very Heavy - at 20 weeks gestation


 If complications occur, transfer to a sedentary job, elimination of strenuous work (especially heavy lifting), elevation of legs during the day, shortened work hours, and extended leave may be required.

 Please refer to other MDA monographs for work after spontaneous miscarriage and cases of induced abortion.

The Characteristics of Uterine Contraction in Labor

The musculature of the pregnant uterus is arranged in three strata:

An external hood-like layer which arches over the fundus and extends into the various ligaments.

An internal layer consisting of sphincter-like fibers around the orifices of the tubes and the internal os.

Lying between the two, a dense network of muscle fibers perforated in all directions by blood vessels. The main portion of the uterine wall is formed by this middle layer which consists of an interlacing network of muscle fibers between which extend the blood vessels. As the result of such an arrangement, when the cells contract after delivery, they constrict the vessels and thus act a "living ligatures."

Uterine contractions are involuntary and, for the most part, independent of extrauterine control. It has been demonstrated that the uterus has pacemakers to produce the rhythmic coordinated contractions of labor. These pacemaker sites are found near the uterotubal junctions, although the pacemaker cells do not differ anatomically from the surrounding myocytes as they do in cardiac muscle. The interval between contractions diminishes gradually from approximately ten minutes in early labor to as little as two minutes near the end of labor. In the normal process there is a progressive increment in the strength of contractions form approximately 20 mm of mercury at the onset of labor to 50 to 80 mm late in labor. The effect of uterine contractions of this frequency and intensity is twofold on the uterine cervix. First effacement consisting of thinning of the cervix with a shortening of the endocervical canal, is produced. Secondly, cervical dilation concurs, initially slowly as it accompanies the process of effacement of the cervix, and then more rapidly as cervical effacement has been accomplished.

Progressive contractile activity of the uterus has been demonstrated throughout pregnancy. Most of these contractions are imperceptible to the pregnant individual, but toward the end of pregnancy they may achieve on a sporadic basis strength equivalent to those of early labor. False labor, Braxton-Hicks contractions, and pre-labor contractions are terms that have been applied to this uterine activity. The latter term is probably the most appropriate, and it is this uterine activity which accomplishes a significant degree of effacement and even some dilatation in the days or weeks prior to the onset of recognizable labor. Descent of the presenting part of the fetus into the birth canal, particularly in a first pregnancy, is another result of pre-labor.

The Mechanism of Normal Labor

The definition or clinical diagnosis of labor is a retrospective one. There is no laboratory test that gives a "labor titer" or an x-ray procedure that can define the difference between the laboring and non-laboring patient. Realizing these limitations, the patient is diagnosed as being in labor when a combination of conditions exist. Perhaps a good working definition may be stated as follows: When in the presence of perceived uterine contractions, there is progressive cervical dilation and descent of the presenting part which leads to the eventual expulsion of the products of conception, the patient is in labor.

The "mechanism of labor" refers to the sequencing of events related to posturing and positioning that allows the baby to find the "easiest way out." For the most part the fetus is a passive respondent in the process of labor, while the mother provides the uterine forces and structural configuration of the passageway through which the passenger must travel. For a normal mechanism of labor to occur, both the fetal and maternal factors must be harmonious. An understanding of these factors is essential for the obstetrician to appropriately intervene if the mechanism deviates from the normal. The following definitions must be mastered to be able to discuss and understand the mechanism of labor:

The single most important determinant to the mechanism of labor is probably pelvic configuration. The classic work of Caldwell and Maloy is reviewed in the text and should be understood. Their classification of the pelvis into four major types (gynecoid, android, anthropoid, and platypelloid) helps the student understand the possible difficulties that may arise in a laboring patient. A quote that should be remembered is: "No two pelves are exactly the same, just as no two faces are the same. For each pelvis there is an optimum mechanism that may be wholly different from the so-called normal mechanism described."

An important principle is that most pelves are not purely defined but occur in nature as mixed types. Regardless of the shape, the baby will be delivered if size and positioning remain compatible. The narrowest part of the fetus attempts to align itself with the narrowest pelvic dimension (e.g., biparietal to interspinous diameters) which means the occiput generally tends to rotate to the "most ample portion of the pelvis."

The mechanical steps the baby undergoes can be arbitrarily divided, and clinically they are usually broken down into six or eight steps for ease of discussion. It must be understood, however, that these are arbitrary distinctions in a natural continuum.

Abnormal mechanisms of labor do occur, and the operator must be able to recognize these early and intervene when appropriate. The above mechanisms of labor should be come "second nature" to the practitioner and indeed does become such by careful observation. Those patients who have undeliverable or uncorrectable problems should be unhesitatingly delivered by the abdominal route because inappropriate operative vaginal intervention may lead to damage to both mother and fetus. Some of the undeliverable situations include persistent mentum posterior, persistent brow presentation, some types of breech presentations, and shoulder presentation. (See Figure)

Normal labor

Emanuel Friedman in his elegant treatise on labor (1978) stated correctly 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 decent, none of the clinical features of the parturient patient appears to be useful in assessing labor progression." Friedman sought to select criteria that would limit normal labor and thus be able to identify significant abnormalities of labor. These limits, admittedly arbitrary, appear to be logical and clinically useful. The graphic representation of labor plotting descent and dilatation against time has become known as the Friedman curve. It, or a modification of it, is used extensively to evaluate laboring patients.

Graphic portrayal of the relationship between cervical dilatation and elapsed time in labor (heavy line) and between fetal station and time (light line). Labor has been divided functionally into a preparatory division (including latent and acceleration phases of the dilatation curve), a dilatational division comprising only the linear phase of maximum slope of dilatation, and a pelvic division encompassing the linear phase of maximum descent.

Functional classification of labor

Principal Clinical Features on the Functional Divisions of Labor

Characteristic      Preparatory Division    Dilatational Division     Pelvic Division

Functions   Contractions coordinated, polarized, oriented; cervix prepared     Cervix actively dilated        Pelvis negotiated; mechanisms of labor; fetal descent; delivery

Interval       Latent and acceleration phases        Phase of maximum slope       Deceleration phase and second stage

Measurement       Elapsed duration Linear rate of dilatation Linear rate of descent

Diagnosable disorders   Prolonged latent phase  Protracted dilatation; protracted descent          Prolonged deceleration; secondary arrest of dilatation; arrest of descent; failure of descent

Abnormal labor

Dystocia (literally difficult labor) is characterized by abnormally slow progress in labor. It is the consequence of four distinct abnormalities that may exist singly or in combination.

Uterine forces that are not sufficiently strong or appropriately coordinated to efface and dilate the cervix.

Forces generated by voluntary muscles during the second stage of labor that are inadequate to overcome the normal resistance of the bony birth canal and maternal soft parts.

Faulty presentation or abnormal development of the fetus of such character that the fetus cannot be extruded through the birth canal.

Abnormalities of the birth canal that form an obstacle to the descent of the fetus.

Labor Disorders

Pattern       Diagnostic Criterion

Prolonged latent phase  Nulliparas 20 hr or more Multiparas 14 hr or more

 Protracted active phase dilatation   Nulliparas 1.2 cm/hr or less

 Protracted descent        Nulliparas 1 cm/hr or less Multiparas 2 cm/hr or less

 Prolonged deceleration phase         Nulliparas 3 hr or more Multiparas 1 hr or more

 Secondary arrest of dilatation         Arrest 2 hr or more

 Arrest of descent Arrest 1 hr or more

 Failure of descent         No descent in deceleration phase of second stage

Prolonged latent phase of labor

Etiologic factors that appear to be responsible for the development of prolonged latent phase disorders in multiparas most often include excessive sedation administered during the course of the latent phase and poor prelabor soft-tissue preparation. In addition, false labor and myometrial dysfunction are found but can be diagnosed only retrospectively.

Arrest disorder

 Secondary arrest of dilatation pattern with documented cessation of progression in the active phase

Prolonged deceleration phase pattern with deceleration phase duration greater than normal limits

Failure of descent in the deceleration phase and second stage

Arrest of descent characterized by halted advancement of fetal station in the second stage.

These four abnormalities are similar in etiology, response to treatment, and prognosis, being readily differentiated from the normal dilatation and descent curves (broken lines).

Etiology of arrest disorders are as follows. The striking association with cephalopelvic disproportion makes these disorders especially ominous; whenever encountered, arrest patterns should signal the likelihood that a bony impediment exists. Other factors very often occur in combination with each other and with disproportion as well.

Take Home Points

The progress of labor is measured by evaluating dilatation of the cervix and descent of the presenting part as a function of time. When an abnormality is diagnosed, the cause is identified and the appropriate treatment initiated.

Labour and delivery are unique experiences in a woman’s life. If not dealt with well, it can lead to unpleasant experiences and mental agony.

 Society punished women by denying them the right to a pain free delivery for a very long time, until the breakthrough in 1853, when Sir John Snow first gave Chloroform to Queen Victoria for the birth of her 8th child Prince Leopold.

Labour is a complex and highly individual process, not every women wants or needs analgesia (pain relief) for delivery. Educating the women during the course of pregnancy, whenever possible is the best option for helping them to make an informed decision. The decision to receive any form of pain relief is personal and should be made by the patient.

The optimal pain relif for labour is one that can provide pain relief for first and second stage of labour with minimal effects on mother and baby. The ideal  technique should provide effective and rapid onset of pain relief with minimal muscle paralysis, long duration, minimal risk of material toxicity and minimal placental transfer and effects on the baby.

Neuraxial labour analgesia (epidural, spinal or combined spinal - epidural analgesia) is currently the most effective method of providing labour analgesia.

What is Labour Analgesia?

Its a method of pain relief for delivery which abolishes the pain without interfering with the uterine contractions which are necessary for the expulsion of the fetus.

What are the techniques of Labour Analgesia?

Attempts to minimize the pain of labour non-pharmacologically first began in the early 20th century. It was suggested that the pain of child birth was brought about by fear and tension and recommended passive muscle relaxation to reduce the pain.

Psychoprophylaxis is a technique which involves educating the mother about the functioning of her body and the physiology of labour.  Other techniques involve simple emotional support from the patient’s partner or another labour companion, touch and massage, the application of hot or cold compresses and hydrotherapy.

 Some techniques require fairly extensive preparation and antenatal training. These include Biofeedback, Acupuncture, Hypnosis and Transcutaneous nerve stimulation (TENS). TENS involves the application of a variable electrical stimulus to the skin at the site of pain . Great or considerable relief of labour pain is seen in 20-24% of mothers with about 60% having slight relief.

Systemic drugs

All drugs given systemically will cross the placenta to reach the baby to some extent.

Pethidine is the most commonly used opiate in obstetric practice.  Intramuscular pethidine 100mg or 150mg was deemed satisfactory by only 22.4% of women in first stage of labour and in 47.7% it gave no relief at all. Nausea and vomiting occur in 50% of patients and exerts both immediate and long term effects on baby.

Morphine is a powerful opiate to pethidine. It benefits from the ability to allay anxiety and longer duration of analgesic action but frequently causes nausea and vomiting and is a potent depressor of baby.

Benzodiazepines are used for maternal sedation. Most commonly used benzodiazepines ia Diazepam but has  side effects on baby which includes decreased muscle tone, decreased activity, respiratory depression . Now a days benzodiazepines are not indicated for pain relief during pregnancy

Pentazocine ( commonly known as fortwin ) is popular drug( medicine) and obstetricians commonly use it because when used in multiple doses does not produce much changes in the  Apgar scores in babies as compared to pethidine. In addition the fetal heart rate is not so affected by pentazocine as it is with pethidine. The chief drawback of pentazocine is unpleasant hallucinogenic side effects and the limited pain relief that it can produce.

Ketamine has been used to produce analgesia during labour, doses in the range of 0.25mg/kg reportedly produce effective analgesia without any adverse effect on uterine blood flow, uterine activity or neonatal status.


Inhalational agents

Inhalational agents  are anaesthetic gases which the labouring women has to inhale(smell) periodically to get pain relief.

Trichloroethylene commonly causes nausea and vomiting and its sweet smell may be unpleasant. Its use in labour is now uncommon.

Analgesia produced by Methoxyflurane persists into the period after inhalation ceases. Nausea and vomiting are uncommon and although inorganic fluoride concentrations are increased in both mother and infant, the risk of renal damage seems negligible as long as inhalation is restricted to low concentrations for limited periods. Again its use in labour is now uncommon. 

Entonox which is 50 : 50 prepared mixture of nitrous oxide and oxygen  is employed as a self administered intermittent inhalation which if used in the correct manner can produce acceptable levels of analgesia.   It should be possible for 40 - 82% of mother to obtain substantial benefit from Entonox when properly managed by the staff.

Peripheral nerve blockade

Peripheral nerve blockade means blocking of the nerve fibers at the periphery which supply the uterus.

Paracervical block can be of value in the first stage of labour. It provides successful analgesia in approximately 80% of mothers. However in the first few minutes after initiating a block a high incidence of fetal bradycardia (decrease in heart rate) associated with a falling pH and oxygen tension have been seen. It has been suggested that the block should be administered in well spaced stages in order to minimize these effects. This complication has led to a marked diminution of its use worldwide.

Pudendal nerve block is almost always used to facilitate operative vaginal delivery and is usually performed by the obstetrician. Local infiltration of the perineum may be necessary  because  bilateral pudendal nerve block was not totally effective in nearly 50% of cases.

Lumbar epidural block

Lumbar epidural blockade is currently the gold standard for pain relief in obstetrics. Epidural analgesia provides the most effective form of pain relief devised so far for labour and delivery. The establishment of an epidural service requires committed individuals and the presence of an anaesthetist in the labour ward, as well as equipment and staff education.

Caudal extradural block

Caudal extradural block is useful in the late first stage and second stage of labour. It provides good relaxation of the perineal muscles. Problems include a relatively high forceps rate, attributed to abnormalities of rotation of the fetal head due to relaxation of the pelvic floor.

Intrathecal block

Single shot spinal have limited utility in early labour and are more useful in the second stage of labour. It is an easier block than epidural blockade and provides good relaxation for the pelvic musculature. Disadvantages cited include post dural puncture headaches. However its incidence is low with the use of fine pencil point (26 or 27G) needles.

Combined Spinal Epidural (CSE)

Since the introduction of this technique in the early 1980’s it has gained increasing popularity for analgesia and anaesthesia in labour and delivery. Because CSE allows for ambulation of the parturient it has been called the Walking Epidural.

What is Epidural Space?

The epidural space lies just outside the special covering or dura, which encloses the spinal canal. An 'epidural' is a type of regional anesthesia in which a needle is positioned between the bones of the spine to allow the anesthesiologist to insert a small plastic tube (or catheter) into the epidural space. The needle is then removed and local anesthetic is injected through the catheter. This local anesthetic moves (or diffuses) across the dura. into the spinal canal, and temporarily stops the spinal nerves from working, so that sensation and movement in the area supplied by the nerves does not occur. When the effect of the local anesthetic wears off, sensation and movement will return. If a weaker solution of local anesthetic is used, then only painful sensations will be blocked. This is very useful for controlling pain and is called epidural analgesia. Often continuous infusions of local anesthetic solutions are used, which allows the effect to be maintained as long as required.  . This is a very useful and safe procedure, when performed with appropriate care by an experienced anesthesiologist.

What are the indications and contraindications for Labour Epidural Analgesia?



1.    Painful Labour

2.    Incoordinate uterine action

3.    Pregnancy induced hypertension

4.    Cardiac diseases

5.    Premature Labour

6.    Multiple Births

7.    Diabetes Mellitus

8.    Asthma and respiratory diseases

9.    Neurovascular diseases

10.                       Prolonged labour


1.    Prematurity

2.    Breech presentation

3.    Multiple gestation



1.    Patient refusal

2.    Local sepsis

3.    Severe anemia

4.    Coagulopathy

5.    Hypovolaemia

6.    Fixed cardiac output state

7.    Inability to cooperate


1.    Pre-existing neurological disease

2.    Severe deformity of spine

What are the advantages of Epidural Obstetric Analgesia?

In obstetric units where successful epidural service is established almost any medical or obstetric complication may be regarded as an indication for regional analgesia. This is largely because it may be desirable to avoid both the stress of painful labour and the risk of general anaesthesia should operative delivery be necessary.

Pain relief

 It is a single most important indication for epidural analgesia, which not only provides physiological benefits to both mother and baby but also makes a labouring women more comfortable, less fatigued and therefore more cooperative.


 Pregnancy induced hypertension is the commonest obstetric indication for epidural analgesia. Epidural blockade is of little value in the absence of pain but in labour it has generally been found to control hypertension successfully and better than hydralazine and magnesium sulphate (commonly prescribed medicines for contol of blood pressure in pregnancy).  Epidural analgesia  produces favorable hemodynamic changes  and a consistent improvement in blood flow to the baby. Complete analgesia could minimize the chance of fits assosiated with pregnancy induced hypertension . Moreover general anaesthesia that is particularly risky in the presence of  edema of face can be avoided.

Cardiac disease

These patients have increased chances of having  complication during labour. Epidural pain relief can minimize the adverse effect of increased blood supply to the heart (which should be avoided in these patients) due to pain or anxiety

Pulmonary disease

Epidural analgesia is of benefit in chest disease because it avoids increases in respiratory rate associated with painful contraction.

Trial of labour

Trial of labour means giving a trial for normal delivery in patients who have undergone caesarean section previously. Epidural analgesia in no way masks the danger of scar  rupture . The pain from the scar and pain from the uterine contractions are felt at the same site and the scar is most likely to be stressed during a contraction. Epidural local anaesthetic more readily blocks the pain of uterine contraction   than pathological pain,  so that it may aid in the diagnosis of scar dehiscence. Analgesia given early in these patients may reduce maternal exhaustion and can subsequent1y be converted to epidural anaesthesia in case a caesarean section is warranted.

Conversion to obstetric anaesthesia

 If an epidural catheter is already insitu, in the event of fetal distress or any need of caesarean section; it can easily be converted to anaesthesia by simply altering the dose of the drug, and the position of the patient, thus, saving time and effort.

Preterm labour and Twin Pregnancy

Epidural analgesia is associated with reduced neonatal mortality rate among low birth weight babies  Likewise the outlook in twin pregnancy particularly for the second twin is improved

Benefit in incoordinate uterine action

By decreasing the catecholamine (adrenal hormone) secretion associated with labour pain, epidural block can improve uterine contractility and rhythmicity and is especially indicated in cases of incoordinate uterine action.

Fetal indications

 Preterm fetus, Breech Presentation & Multiple Pregnancy - 

 In these conditions an epidural block allows a more controlled delivery because of relaxed pelvic floor muscles and a decreased urge to push.

Decreased blood loss

 It is evidenced following vaginal delivery under epidural block as compared to delivery without epidural block  This can be explained by the epidural induced peripheral  pooling of blood in legs and thus decreased cardiac output .

What are the problems associated with Epidural Analgesia?

1.    Hypotension

2.    Backache

3.    Shivering

4.    Urinary retention

5.    Bloody tap

6.    Dural puncture and post dural puncture headache

7.    Total spinal block