Chapter 7. Normal & Abnormal Labor & Delivery

Essentials of Diagnosis

• Labor is a sequence of uterine contractions that results in effacement and dilatation of the cervix and voluntary bearing-down efforts, leading to the expulsion per vagina of the products of conception.
• Delivery is the mode of expulsion of the fetus and placenta.

Pathogenesis

Labor and delivery is a normal physiologic process that most women experience without complications. The goal of the management of this process is to foster a safe birth for mothers and their newborns. Additionally, the staff should attempt to make the patient and her support person(s) feel welcome, comfortable, and informed throughout the labor and delivery process. Physical contact between the newborn and the parents in the delivery room should be encouraged. Every effort should be made to foster family interaction and to support the desire of the family to be together. The role of the obstetrician/midwife and the labor and delivery staff is to anticipate and manage complications that may occur that could harm the mother or the fetus. When a decision is made to intervene, it must be considered carefully, because each intervention carries both potential benefits and potential risks. The best management in the majority of cases may be close observation and, when necessary, cautious intervention.

Physiologic Preparation for Labor

Before the onset of true labor, several preparatory physiologic changes commonly occur. The settling of the fetal head into the brim of the pelvis, known as lightening, usually occurs 2 or more weeks before labor in first pregnancies. In women who have had a previous delivery, lightening often does not occur until early labor. Clinically, the mother may notice a flattening of the upper abdomen and increased pressure in the pelvis. This descent of the fetus is often accompanied by a decrease in discomfort associated with crowding of the abdominal organs under the diaphragm (eg, heartburn, shortness of breath) and an increase in pelvic discomfort and frequency of urination.

During the last 4–8 weeks of pregnancy, irregular, generally painless uterine contractions occur with slowly increasing frequency. These contractions, known as Braxton Hicks contractions, may occur more frequently, sometimes every 10–20 minutes, and with greater intensity during the last weeks of pregnancy. When these contractions occur early in the third trimester, they must be distinguished from true preterm labor. Later, they are a common cause of “false labor,” which is distinguished by the lack of cervical change in response to the contractions.

During the course of several days to several weeks before the onset of true labor, the cervix begins to soften, efface, and dilate. In many cases, when labor starts, the cervix is already dilated 1–3 cm in diameter. This is usually more pronounced in the multiparous patient, the cervix being relatively more firm and closed in nulliparous women. With cervical effacement, the mucus plug within the cervical canal may be released. When this occurs, the onset of labor is sometimes marked by the passage of a small amount of blood-tinged mucus from the vagina known as bloody show.

Mechanism of Labor

The mechanism of labor in the vertex position consists of engagement of the presenting part, flexion, descent, internal rotation, extension, external rotation, and expulsion (Table 7–1). The progress of labor is dictated by the pelvic dimensions and configuration, the size of the fetus, and the strength of the contractions. In essence, delivery proceeds along the line of least resistance, that is, by adaptation of the smallest achievable diameters of the presenting part to the most favorable dimensions and contours of the birth canal.

The sequence of events in vertex presentation is as follows:

Engagement

This usually occurs late in pregnancy in the primigravida, commonly in the last 2 weeks. In the multiparous patient, engagement usually occurs with the onset of labor. The head enters the superior strait in the occiput transverse position in 70% of women with a gynecoid pelvis (Figs. 7–1 and 7–2).

Flexion

In most cases, flexion is essential for both engagement and descent. This will vary, of course, if the head is small in relation to the pelvis or if the pelvis is unusually large. When the head is improperly fixed—or if there is significant narrowing of the pelvic strait (as in the platypelloid type of pelvis)—there may be some degree of deflexion, if not actual extension. Such is the case with a brow (deflexion) or face (extension) presentation.

Descent

Descent is gradually progressive and is affected by the forces of labor and thinning of the lower uterine segment. Other factors also play a part (eg, pelvic configuration and the size and position of the presenting part). The greater the pelvic resistance or the poorer the contractions, the slower the descent. Descent continues progressively until the fetus is delivered; the other movements are superimposed on it (Fig. 7–3).

Internal Rotation

With the descent of the head into the midpelvis, rotation occurs so that the sagittal suture occupies the anteroposterior diameter of the pelvis. Internal rotation normally begins with the presenting part at the level of the ischial spines. The levator ani muscles form a V-shaped sling that tends to rotate the vertex anteriorly. In cases of occipitoanterior vertex, the head has to rotate 45 degrees, and in occipitoposterior vertex, 135 degrees, to pass beneath the pubic arch (Fig. 7–4).

Extension

Because the vaginal outlet is directed upward and forward, extension must occur before the head can pass through it. As the head continues its descent, there is a bulging of the perineum, followed by crowning. Crowning occurs when the largest diameter of the fetal head is encircled by the vulvar ring (Fig. 7–5). At this time, spontaneous delivery is imminent.

External Rotation

External rotation (restitution) follows delivery of the head when it rotates to the position it occupied at engagement. After this, the shoulders descend in a path similar to that traced by the head. The anterior shoulder rotates internally approximately 45 degrees to come under the pubic arch for delivery (Fig. 7–6). As this occurs, the head swings back to its position at birth.

Clinical Findings

In true labor, the woman is usually aware of her contractions during the first stage. The intensity of pain depends on the fetal/pelvic relationships, the quality and strength of uterine contractions, and the emotional and physical status of the patient. Few women experience no discomfort during the first stage of labor. Some women describe slight low back pain that radiates around to the lower abdomen. Each contraction starts with a gradual build-up of intensity, and dissipation of discomfort promptly follows the climax. Normally, the contraction will be at its height well before discomfort is reported. Dilatation of the lower birth canal and distention of the perineum during the second stage of labor will almost always cause discomfort.

Normal labor is a continuous process that has been divided into three stages for purposes of study, with the first stage further subdivided into two phases, the latent phase and the active phase.

• The first stage of labor is the interval between the onset of labor and full cervical dilatation.
• The second stage is the interval between full cervical dilatation and delivery of the infant.
• The third stage of labor is the period between the delivery of the infant and the delivery of the placenta.

In his classic studies of labor in 1967, Friedman presented data describing the process of spontaneous labor over time. The duration of the first stage of labor in primipara patients is noted to range from 6–18 hours, whereas in multiparous patients, the range is reported to be 2–10 hours. The lower limit of normal for the rate of cervical dilatation during the active phase is 1.2 cm per hour in first pregnancies and 1.5 cm per hour in subsequent pregnancies. The duration of the second stage in the primipara is 30 minutes to 3 hours and is 5–30 minutes for multiparas. For both, the duration of the third stage was reported to be 0–30 minutes for all pregnancies. These data, although extremely helpful as guidelines, should not be used as strict deadlines that trigger interventions if not met. Even if a numerical (statistical) approach is used to define “abnormal,” the cutoff figure would not be the average range, but the 5th percentile numbers (eg, 25.8 hours for the first stage of labor in a primipara). The course that is more appropriate is to consider the overall clinical presentation and use the progress of labor to estimate the likelihood that successful vaginal delivery will occur.

The first stage of labor is evaluated by the rate of change of cervical effacement, cervical dilatation, and descent of the fetal head. The frequency and duration of uterine contractions alone is not an adequate measure of labor progress. The second stage of labor begins after full cervical dilatation. The progress of this stage is measured by the descent, flexion, and rotation of the presenting part.

Treatment

Women most likely to have a normal labor and delivery have had adequate prenatal care without significant maternal or fetal complications and are at 36 weeks' gestation or beyond. Whenever a pregnant woman is evaluated for labor, the following factors should be assessed and recorded:

• Time of onset and frequency of contractions, status of membranes, any history of bleeding, and any fetal movement.
• History of allergies, use of medication, and time, amount, and content of last oral intake.
• Prenatal records with special attention to prenatal laboratory results that impact intrapartum and immediate postpartum management (eg, HIV and hepatitis B status).
• Maternal vital signs, urinary protein and glucose, and uterine contraction pattern.
• Fetal heart rate, presentation, and clinical estimated fetal weight.
• Status of the membranes, cervical dilatation and effacement (unless contraindicated, eg, by placenta previa), and station of the presenting part.

If no complications are detected during the initial assessment and the patient is found to be in prodromal labor, admission for labor and delivery may be deferred. When a patient is admitted, a hematocrit or hemoglobin measurement should be obtained and a blood clot should be obtained in the event that a cross-match is needed. A blood group, Rh type, and antibody screen should also be done.

The First Stage of Labor

In the first stage of normal labor, the pregnant woman may be allowed to ambulate or sit in a comfortable chair as desired. When the patient is lying in bed, the supine position should be discouraged. Patients in active labor should avoid ingestion of solid food. Clear liquids, ice chips, or preparations for moistening the mouth and lips should be allowed. When significant amounts of fluids and calories are required because of long labor, they should be given intravenously.

Maternal pulse and blood pressure should be recorded at least every 2–4 hours in normal labor and more frequently if indicated. Maternal fluid balance (ie, urine output and intravenous and oral intake) should be monitored, and both dehydration and fluid overload should be avoided.

Management of discomfort and pain during labor and delivery is a necessary part of good obstetric practice. A patient's request is sufficient justification for providing pain relief during labor. Specific analgesic and anesthetic techniques are discussed in Chapter 24. Some patients tolerate the pain of labor by using techniques learned in childbirth preparation programs. Common methods of preparation include Lamaze, Bradley, Read, hypnotherapy, and prenatal yoga. Although specific techniques vary, these classes usually teach relief of pain through the application of principles of education, emotional support, touch, relaxation, paced breathing, and mental focus. The staff at the bedside should be knowledgeable about these pain-management techniques and should be supportive of the patient's decision to use them. When such methods fail to provide adequate pain relief, some patients will ask for medical assistance, and such requests should be respected. Indeed, the use of appropriate medical analgesic techniques should be explained to the patient and her labor partner and their use encouraged when medically indicated.

Reassurance of fetal well-being is sought through fetal monitoring. Fetal monitoring may be performed intermittently or continuously, depending on the presence or absence of risk factors for adverse perinatal outcome. In patients with no significant obstetric risk factors, either continuous or intermittent monitoring is acceptable. If the fetus is monitored intermittently, then the fetal heart rate should be auscultated or the electronic monitor tracing should be evaluated at least every 30 minutes in the active phase of the first stage of labor and at least every 15 minutes in the second stage of labor. In patients with obstetric risk factors such as hypertension, intrauterine fetal growth restriction, diabetes, or multiple gestations, continuous fetal monitoring is recommended.

Uterine contractions may be monitored by palpation, by tocodynamometer, or by internal pressure catheter. If monitored by palpation, the patient's abdomen should be palpated every 30 minutes to assess contraction frequency, duration, and intensity. For at-risk pregnancies, uterine contractions should be monitored continuously along with the fetal heart rate. This can be achieved by using either an external tocodynamometer or an internal pressure catheter in the amniotic cavity. The latter method is particularly useful when abnormal progression of labor is suspected or when the patient requires oxytocin for augmentation of labor.

The progress of labor is monitored by examination of the cervix. During the latent phase, especially when the membranes are ruptured, vaginal examinations should be done sparingly to decrease the risk of intrauterine infection. In the active phase, the cervix should be assessed approximately every 2 hours. The cervical effacement and dilatation and the station and position of the fetal head should be recorded (Fig. 7–7). Additional examinations to determine whether full dilation has occurred may be required if the patient reports the urge to push, or to search for prolapse of the umbilical cord or perform fetal scalp stimulation if a significant fetal heart rate deceleration is detected.

The therapeutic rupture of fetal membranes (amniotomy) has been largely discredited as a means of induction when used alone. Moreover, artificial rupture of the membranes increases the risk of chorioamnionitis and the need for antibiotics (especially if labor is prolonged), as well as the risk of cord prolapse if the presenting part is not engaged. Amniotomy may, however, provide information on the volume of amniotic fluid and the presence of meconium. In addition, rupture of the membranes may cause an increase in uterine contractility. Amniotomy should not be performed routinely. It should be used when internal fetal or uterine monitoring is required and may be helpful when enhancement of uterine contractility in the active phase of labor is indicated. Care should be taken to palpate for the umbilical cord and to avoid dislodging the fetal head. The fetal heart rate should be recorded before, during, and immediately after the procedure.

The Second Stage of Labor

At the beginning of the second stage of labor, the mother usually feels a desire to bear down with each contraction. This abdominal pressure, together with the force of the uterine contractions, expels the fetus. During the second stage of labor. the descent of the fetal head is measured to assess the progress of labor. The descent of the fetus is evaluated by measuring the relationship of the bony portion of the fetal head to the level of the maternal ischial spines (station) (Fig. 7–7). When the leading portion of the fetal skull is at the level of the ischial spines, the station is “0.” The American College of Obstetricians and Gynecologists–endorsed method for describing station is to estimate the number of centimeters from the ischial spines. For instance, when the leading portion of the head is 2 cm above the ischial spines, this is reported as −2 station; when the leading portion of the skull is 3 cm below the ischial spines, this is reported as +3. Some practitioners find it useful to refer to station in estimated thirds of the maternal pelvis. An approximate correlation of these two methods would be as follows: 2 cm = +1, 4 cm = +2, and 6 cm = +3.

The second stage generally takes from 30 minutes to 3 hours in primigravid women and from 5–30 minutes in multigravid women. The median duration is 50 minutes in a primipara and 20 minutes in a multipara. These times may vary depending on the pushing efforts of the mother, the quality of the uterine contractions, and the type of analgesia.

Delivery

When the fetal head is noted to crown, delivery is imminent. Careful management by the practitioner with controlled efforts of the mother will minimize perineal trauma. Routine episiotomy is unnecessary and is associated with increased maternal blood loss, increased risk of disruption of the anal sphincter (third-degree extension) and rectal mucosa (fourth-degree extension), and delay in the patient's resumption of sexual activity. Further extension follows extrusion of the head beyond the introitus. Once the head is delivered, the airway is cleared of blood and amniotic fluid using a bulb suction device. The oral cavity is cleared initially, followed by clearing of the nares.

After the airway is cleared, an index finger is used to check whether the umbilical cord encircles the neck. If so, the cord can usually be slipped over the infant's head. If the cord is too tight, it can be cut between two clamps.

Delivery of the anterior shoulder is aided by gentle downward traction on the externally rotated head (Fig. 7–8). The posterior shoulder is then delivered by gentle upward traction on the head (Fig. 7–9). The brachial plexus may be injured if excessive force is used. After these maneuvers, the body, legs, and feet are delivered with gentle traction on the shoulders.

After delivery, blood will be infused from the placenta into the newborn if the baby is held below the mother's introitus. Delayed cord clamping can result in neonatal hyperbilirubinemia as additional blood is transferred to the newborn infant. Generally, a vigorous newborn can be delivered directly from the introitus to the abdomen and waiting arms of a healthy, alert mother. Placing the child skin to skin (abdomen to abdomen) results in optimum warmth for the newborn. Then the cord, which has been doubly clamped, may be cut between the clamps by either the practitioner, the mother, or her partner.

Third Stage of Labor

Immediately after the baby is delivered, the cervix and vagina should be inspected for actively bleeding lacerations and surgical repair should be performed as needed. Repair of vaginal lacerations should be performed using absorbable suture material, either 2-0 or 3-0. The inspection and repair of the cervix, vagina, and perineum is often easier prior to the separation of the placenta before uterine bleeding obscures visualization.

Separation of the placenta generally occurs within 2–10 minutes of the end of the second stage, but it may take 30 minutes or more to spontaneously separate. Signs of placental separation are as follows: (1) a fresh show of blood appears from the vagina, (2) the umbilical cord lengthens outside the vagina, (3) the fundus of the uterus rises up, and (4) the uterus becomes firm and globular. When these signs appear, it is safe to place traction on the cord. The gentle traction, with or without counterpressure between the symphysis and fundus to prevent descent of the uterus, allows delivery of the placenta.

After the delivery of the placenta, attention is turned to prevention of excessive postpartum bleeding. Uterine contractions that reduce this bleeding may be enhanced with uterine massage and/or the infusion of a dilute solution of oxytocin. The placenta should be examined to ensure complete removal and to detect placental abnormalities.

Puerperium

The puerperium consists of the period after the delivery of the baby and placenta to approximately 6 weeks postpartum. The immediate postpartum period (within the first hour of delivery) is a critical time for both maternal and neonatal physiologic and emotional adjustment. During that hour, the maternal blood pressure, pulse rate, and uterine blood loss must be monitored closely. It is during this time that most postpartum hemorrhage usually occurs, largely as a result of uterine relaxation, retained placental fragments, or unrepaired lacerations. Occult bleeding (eg, vaginal wall hematoma formation) may manifest as increasing pelvic pain.

At the same time, maternal bonding to the newborn is evolving, and ideally breastfeeding is initiated. Early initiation of breastfeeding is beneficial to the health of both the mother and the newborn. Both benefit because babies are extremely alert and programmed to latch onto the breast during this period. Mother–infant pairs that begin breastfeeding early are most able to continue breastfeeding for longer periods of time. For the mother, nursing accelerates the involution of the uterus, thereby reducing blood loss by increasing uterine contractions. For the newborn, there are important immunologic advantages. For example, various maternal antibodies are present in breast milk, which provide the newborn with passive immunity against certain infections. Also immunoglobulin (Ig) A, a secretory immunoglobulin present in significant amounts in breast milk, protects the infant's gut by preventing attachment of harmful bacteria to cells of the gut mucosal surface. It is also believed that maternal lymphocytes pass through the infant's gut wall and initiate immunologic processes that are not yet fully understood. In addition to the immunologic benefits, breast milk is the ideal nutritional source for the newborn. Moreover, it is inexpensive and is usually in good supply. Given all the advantages (the preceding is only a partial list of the benefits), encouraging successful breastfeeding is an important health goal.

Induction and Augmentation of Labor

Induction of labor is the process of initiating labor by artificial means; augmentation is the artificial stimulation of labor that has begun spontaneously. Labor induction should be performed only after appropriate assessment of the mother and fetus. Additionally, the risks, benefits, and alternatives to induction in each case must be evaluated and explained to the patient. In the absence of medical indications for induction, fetal maturity must be confirmed by either exact pregnancy dating, first-trimester ultrasound measurements, and/or amniotic fluid analysis. Evaluation of the cervical status in terms of effacement and softening is important in predicting success of induction and is highly recommended before any elective induction (Table 7–2). Generally, induction should be done in response to specific indications and should not be done electively prior to 39 weeks gestational age.

Indications

The following are common indications for induction of labor:

Maternal

—Preeclampsia, diabetes mellitus, heart disease.

Fetal

—Prolonged pregnancy, Rh incompatibility, fetal abnormality, chorioamnionitis, premature rupture of membranes, placental insufficiency, suspected intrauterine growth restriction.

Contraindications

Absolute contraindications to induction of labor include contracted pelvis; placenta previa; uterine scar because of previous classical caesarean section, myomectomy entering the endometrium, hysterotomy, or unification surgery; and transverse lie.

Labor induction should be carried out with caution in the following situations: breech presentation, oligohydramnios, multiple gestation, grand multiparity, previous caesarean section with transverse scar, prematurity, suspected fetal macrosomia.

Complications of Induction of Labor

For the Mother

In many cases, induction of labor exposes the mother to more distress and discomfort than judicious delay and subsequent vaginal or caesarean delivery. The following hazards must be kept in mind: (1) failure of induction with increased risk of caesarean delivery; (2) uterine inertia and prolonged labor; (3) tumultuous labor and tetanic contractions of the uterus, causing premature separation of the placenta, rupture of the uterus, and laceration of the cervix; (4) intrauterine infection; and (5) postpartum hemorrhage.

For the Fetus

An induced delivery exposes the infant to the risk of prematurity if the estimated date of conception has been inaccurately calculated. Precipitous delivery may result in physical injury. Prolapse of the cord may follow amniotomy. Injudicious administration of oxytocin or inadequate observation during induction could lead to fetal heart rate abnormalities or delivery of a baby with poor Apgar scores.

Methods of Cervical Ripening

Cervical ripening before induction of labor could facilitate the onset and progression of labor and increase the chance of vaginal delivery, particularly in primigravid patients.

Prostaglandin

Two forms of prostaglandins are commonly used for cervical ripening before induction at term: misoprostol (PGE1) and dinoprostone (PGE2). Although only dinoprostone, commercially available as prostaglandin gel, is currently Food and Drug Administration–approved for this use, off-label use of misoprostol for cervical ripening is widely practiced. Indeed, although both misoprostol and dinoprostone applied locally intravaginally can provide significant improvement in the Bishop score, a meta-analysis of randomized, controlled trials focusing on cervical ripening and induction of labor found the time to delivery was shorter and the rate of caesarean delivery was lower in the misoprostol group.

Dinoprostone comes prepackaged in a single-dose syringe containing 0.5 mg of PGE2 in 2.5 mL of a viscous gel of colloidal silicon dioxide in triacetin. The syringe is attached to a soft-plastic catheter for intracervical administration, and the catheter is shielded to help prevent application above the internal cervical os. Misoprostol is manufactured in 100-μg unscored and 200-μg scored tablets that can be administered orally, vaginally, and rectally. PGE2 should not be used in patients with a history of asthma, glaucoma, or myocardial infarction. Unexplained vaginal bleeding, chorioamnionitis, ruptured membranes, and previous caesarean section are relative contraindications to the use of prostaglandins for cervical ripening.

For cervical ripening and induction at term, misoprostol is given vaginally at a dose of 25 μg every 4–6 hours. With dinoprostone, usually 12 hours should be allowed for cervical ripening, after which oxytocin induction should be started. PGE1 and PGE2 have similar side-effect and risk profiles, including fetal heart rate deceleration, fetal distress, emergency caesarean section, uterine hypertonicity, nausea, vomiting, fever, and peripartum infection. However, a current literature review does not indicate any significant differences in reported side effects between control and treatment groups with prostaglandin cervical ripening.

Balloon Catheter

A Foley catheter with a 25- to 50-mL balloon is passed into the endocervix above the internal os using tissue forceps. The balloon is then inflated with sterile saline, and the catheter is withdrawn gently to the level of internal cervical os. This method should induce cervical ripening over 8–12 hours. The cervix will be dilated 2–3 cm when the balloon falls out, which will make amniotomy possible, but effacement may be unchanged.

Hygroscopic Dilators

Laminaria tents are made from desiccated stems of the cold-water seaweed Laminaria digitata or L japonica. When placed in the endocervix for 6–12 hours, the laminaria increases in diameter 3- to 4-fold by extracting water from cervical tissues, gradually swelling and expanding the cervical canal. Synthetic dilators like lamicel, a polyvinyl alcohol polymer sponge impregnated with 450 mg of magnesium sulfate, and dilapan, which is made from a stable nontoxic hydrophilic polymer of polyacrylonitrile, are also noted to be highly effective in mechanical cervical dilation.

Methods of Induction of Labor

Oxytocin

Intravenous administration of a very dilute solution of oxytocin is the most effective medical means of inducing labor. Oxytocin exaggerates the inherent rhythmic pattern of uterine motility, which often becomes clinically evident during the last trimester and increases as term is approached.

The dosage must be individualized. The administration of oxytocin is determined with a biologic assay: The smallest possible effective dose must be determined for each patient and then used to initiate and maintain labor. Constant observation by qualified attendants is required when this method is used.

In most cases it is sufficient to add 1 mL of oxytocin (10 units of oxytocin to 1 L of 5% dextrose in water [1 mU/mL]). One acceptable oxytocin infusion regimen is to begin induction or augmentation at 1 mU/min, preferably with an infusion pump or other accurate delivery system, and increase oxytocin in 2-mU increments at 15-minute intervals.

When contractions of 50–60 mm Hg (per the internal monitor pressure) or lasting 40–60 seconds (per the external monitor) occur at 2.5- to 4-minute intervals, the oxytocin dose should be increased no further. Oxytocin infusion is discontinued whenever hyperstimulation or fetal distress is identified, but can be restarted when reassuring fetal heart rate and uterine activity patterns are restored.

Amniotomy

Early and variable decelerations of the fetal heart rate are noted to be relatively common with amniotomy. Nonetheless, amniotomy may be an effective way to induce labor in carefully selected cases with high Bishop scores. Release of amniotic fluid shortens the muscle bundles of the myometrium; the strength and duration of the contractions are thereby increased, and a more rapid contraction sequence follows. The membranes should be ruptured with an amniohook. Make no effort to strip the membranes, and do not displace the head upward to drain off amniotic fluid. Because amniotomy has not been proven effective in augmenting labor uniformly, it is recommended that the active phase of labor be entered before performing amniotomy for augmentation. Amniotomy in selected cases, although slightly increasing the risk of infectious morbidity, could shorten the course of labor without increasing or reducing the incidence of operative delivery.