The membrane-occupied spaces between the cranial bones are known as sutures. The sagittal suture lies between the parietal bones and extends in an anteroposterior direction between the fontanelles, dividing the head into right and left sides (Figure 8-1). The lambdoid suture extends from the posterior fontanelle laterally and serves to separate the occipital from the parietal bones. The coronal suture extends from the anterior fontanelle laterally and serves to separate the parietal and frontal bones. The frontal suture lies between the frontal bones and extends from the anterior fontanelle to the glabella (the prominence between the eyebrows).

FIGURE 8-1 Superior view of the fetal skull showing the sutures, fontanelles, and transverse diameters.

Fontanelles

The membrane-filled spaces located at the point where the sutures intersect are known as fontanelles, the most important of which are the anterior and posterior fontanellesClinically, they are even more useful in diagnosing the fetal head position than the sutures.

The posterior fontanelle closes at 6 to 8 weeks of life, whereas the anterior fontanelle does not become ossified until about 18 months. This allows the skull to accommodate the tremendous growth of the infant’s brain after birth.

The anterior fontanelle (bregma) is found at the intersection of the sagittal, frontal, and coronal sutures. It is diamond shaped and measures about 2 × 3 cm, and it is much larger than the posterior fontanelle. The posterior fontanelle is Y- or T-shaped and is found at the junction of the sagittal and lambdoid sutures.

Several diameters of the fetal skull are important (see Figures 8-1 and 8-2). The anteroposterior diameter presenting to the maternal pelvis depends on the degree of flexion or extension of the head and is important because the various diameters differ in length. The following measurements are considered average for a term fetus:

1. Suboccipitobregmatic (9.5 cm), the presenting anteroposterior diameter when the head is well flexed, as in an occipitotransverse or occipitoanterior position; it extends from the undersurface of the occipital bone at the junction with the neck to the center of the anterior fontanelle.

2. Occipitofrontal (11 cm), the presenting anteroposterior diameter when the head is deflexed, as in an occipitoposterior presentation; it extends from the external occipital protuberance to the glabella.

3. Supraoccipitomental (13.5 cm), the presenting anteroposterior diameter in a brow presentation and the longest anteroposterior diameter of the head; it extends from the vertex to the chin.

4. Submentobregmatic (9.5 cm), the presenting anteroposterior diameter in face presentations; it extends from the junction of the neck and lower jaw to the center of the anterior fontanelle.

The transverse diameters of the fetal skull are as follows:

1. Biparietal (9.5 cm), the largest transverse diameter; it extends between the parietal bones.

2. Bitemporal (8 cm), the shortest transverse diameter; it extends between the temporal bones.

The average circumference of the term fetal head, measured in the occipitofrontal plane, is 34.5 cm.

PELVIC ANATOMY

Pelvic Plane	Diameter	Average Length (cm)
Inlet	True (anatomic) conjugate	11.5
	Obstetric conjugate	11
	Transverse	13.5
	Oblique	12.5
	Posterior sagittal	4.5
Greatest diameter	Diagonal conjugate	12.75
	Transverse	12.5
Midplane	Anteroposterior	12
	Bispinous	10.5
	Posterior sagittal	4.5-5
Outlet	Anatomic anteroposterior	9.5
	Obstetric anteroposterior	11.5
	Bituberous	11
	Posterior sagittal	7.5

Pelvic Inlet

The pelvic inlet has five important diameters (Figure 8-3). The anteroposterior diameter is described by one of two measurements. The true conjugate (anatomic conjugate) is the anatomic diameter and extends from the middle of the sacral promontory to the superior surface of the pubic symphysis. The obstetric conjugate represents the actual space available to the fetus and extends from the middle of the sacral promontory to the closest point on the convex posterior surface of the symphysis pubis.

FIGURE 8-3 Pelvic inlet and its diameters.

The transverse diameter is the widest distance between the iliopectineal lines. Each oblique diameter extends from the sacroiliac joint to the opposite iliopectineal eminence.

The posterior sagittal diameter extends from the anteroposterior and transverse intersection to the middle of the sacral promontory.

Plane of Greatest Diameter

The plane of greatest diameter has two noteworthy diameters. The anteroposterior diameter extends from the midpoint of the posterior surface of the pubis to the junction of the 2nd and 3rd sacral vertebrae. The transverse diameter is the widest distance between the lateral borders of the plane.

Plane of Least Diameter (Midplane)

The plane of least diameter has three important diameters. The anteroposterior diameter extends from the lower border of the pubis to the junction of the fourth and fifth sacral vertebrae. The transverse (bispinous) diameter extends between the ischial spines. The posterior sagittal diameter extends from the midpoint of the bispinous diameter to the junction of the fourth and fifth sacral vertebrae.

Pelvic Outlet

The pelvic outlet has four important diameters (Figure 8-4). The anatomic anteroposterior diameter extends from the inferior margin of the pubis to the tip of the coccyx, whereas the obstetric anteroposterior diameter extends from the inferior margin of the pubis to the sacrococcygeal joint. The transverse (bituberous) diameter extends between the inner surfaces of the ischial tuberosities, and the posterior sagittal diameter extends from the middle of the transverse diameter to the sacrococcygeal joint.

FIGURE 8-4 Pelvic outlet and its diameters.

PELVIC SHAPES

Based on the general bony architecture, the pelvis may be classified into four basic types (Figure 8-5).

FIGURE 8-5 The four basic pelvic types. The dotted line indicates the transverse diameter of the inlet. Note that the widest diameter of the inlet is posteriorly situated in an android or anthropoid pelvis. The gynecoid pelvis illustrates the location of the sacrosciatic notch, present in all pelvic types.

Gynecoid

The gynecoid pelvis is the classic female type of pelvis and is found in about 50% of women. It has the following characteristics:

1. Round at the inlet, with the widest transverse diameter only slightly greater than the anteroposterior diameter

2. Side walls straight

3. Ischial spines of average prominence

4. Large sacrospinous notch

5. Well-curved sacrum

6. Spacious subpubic arch, with an angle of about 90 degrees

These features create a cylindrical shape that is spacious throughout. The fetal head generally rotates into the occipitoanterior position in this type of pelvis.

Android

The android pelvis is the typical male type of pelvis, and it is found in less than 30% of women and has the following characteristics:

1. Triangular inlet with a flat posterior segment and the widest transverse diameter closer to the sacrum than in the gynecoid type

2. Convergent side walls with prominent spines

3. Shallow sacral curve

4. Long and narrow (small) sacrospinous notch

5. Narrow subpubic arch

This type of pelvis has limited space at the inlet and progressively less space as one moves down the pelvis, owing to the funneling effect of the side walls, sacrum, and pubic rami. Thus, the amount of space is restricted at all levels. The fetal head is forced to be in the occipitoposterior position to conform to the narrow anterior pelvis. Arrest of descent is common at the midpelvis.

Anthropoid

The anthropoid pelvis resembles that of the anthropoid ape. It is found in about 20% of women and has the following characteristics:

1. A much larger anteroposterior than transverse diameter, creating a long narrow oval at the inlet

2. Side walls that do not converge

3. Ischial spines that are not prominent but are close, owing to the overall shape

4. Variable, but usually posterior, inclination of the sacrum

5. Small sacrospinous notch

6. Narrow, outwardly shaped subpubic arch

The fetal head can engage only in the anteroposterior diameter and usually does so in the occipitoposterior position because there is more space in the posterior pelvis.

Platypelloid

The platypelloid pelvis is best described as being a flattened gynecoid pelvis. It is found in only 3% of women, and it has the following characteristics:

1. A short anteroposterior and wide transverse diameter creating an oval-shaped inlet

2. Straight or divergent side walls

3. Posterior inclination of a flat sacrum

4. A wide bispinous diameter

5. Long but small sacrospinous notch

6. A wide subpubic arch

The overall shape is that of a gentle curve throughout. The fetal head has to engage in the transverse diameter.

ENGAGEMENT

Engagement occurs when the widest diameter of the fetal presenting part has passed through the pelvic inlet. In cephalic presentations, the widest diameter is biparietal; in breech presentations, it is intertrochanteric.

The station of the presenting part in the pelvic canal is defined as its level above or below the plane of the ischial spines. The level of the ischial spines is assigned as “zero” station, and each centimeter above or below this level is given a minus or plus designation, respectively, for a total length of 10 cm.

In most women, the bony presenting part is at the level of the ischial spines when the head has become engaged. The fetal head usually engages with its sagittal suture in the transverse diameter of the pelvis. The head position is considered to be synclitic when the biparietal diameter is parallel to the pelvic plane and the sagittal suture is midway between the anterior and posterior planes of the pelvis. When this relationship is not present, the head is considered to be asynclitic (Figure 8-6).

FIGURE 8-6 Anterior asynclitism entering the pelvis (A), and synclitism in the pelvis (B).

There is a distinct advantage to having the head engage in asynclitism in certain situations. In a synclitic presentation, the biparietal diameter entering the pelvis measures 9.5 cm; but when the parietal bones enter the pelvis in an asynclitic manner, the presenting diameter measures 8.75 cm. Therefore, asynclitism permits a larger head to enter the pelvis than would be possible in a synclitic presentation.

CLINICAL PELVIMETRY

The diameters that can be clinically evaluated can be assessed at the time of the first prenatal visit to screen for obvious pelvic contractions, although some obstetricians believe that it is better to wait until later in pregnancy when the soft tissues are more distensible and the examination is less uncomfortable and possibly more accurate.

The clinical evaluation is started by assessing the pelvic inlet. The pelvic inlet can be evaluated clinically for its anteroposterior diameter. The obstetric conjugate can be estimated from the diagonal conjugate, which is obtained on clinical examination (see Figure 8-3).

The diagonal conjugate is approximated by measuring from the lower border of the pubis to the sacral promontory using the tip of the second finger and the point where the base of the index finger meets the pubis (Figure 8-7). The obstetric conjugate is then estimated by subtracting 1.5 to 2 cm, depending on the height and inclination of the pubis. Often the middle finger of the examining hand cannot reach the sacral promontory; thus, the obstetric conjugate is considered adequate. If the diagonal conjugate is greater than or equal to 11.5 cm, the anteroposterior diameter of the inlet is considered to be adequate.

FIGURE 8-7 Clinical estimation of the diagonal conjugate diameter of the pelvis.

The anterior surface of the sacrum is then palpated to assess its curvature. The usual shape is concave. A flat or convex shape may indicate anteroposterior constriction throughout the pelvis.

The midpelvis cannot accurately be measured clinically in either the anteroposterior or transverse diameter. A reasonable estimate of the size of the midpelvis, however, can be obtained as follows. The pelvic side walls can be assessed to determine whether they are convergent rather than having the normal, almost parallel, configuration. The ischial spines are palpated carefully to assess their prominence, and several passes are made between the spines to approximate the bispinous diameter. The length of the sacrospinous ligament is assessed by placing one finger on the ischial spine and one finger on the sacrum in the midline. The average length is 3 fingerbreadths. If the sacrospinous notch that is located lateral to the ligament can accommodate two-and-a-half fingertips, the posterior midpelvis is most likely of adequate dimensions. A short ligament suggests a forward inclination of the sacrum and a narrowed sacrospinous notch (see Figure 8–5, pg 95).

Finally, the pelvic outlet is assessed. This is done by first placing a fist between the ischial tuberosities. An 8.5-cm distance is considered an adequate transverse diameter. The posterior sagittal measurement should also be greater than 8 cm. The infrapubic angle is assessed by placing a thumb next to each inferior pubic ramus and then estimating the angle at which they meet. An angle of less than 90 degrees is associated with a contracted transverse diameter in the midplane and outlet.

Radiologic Assessment of the Pelvis

When an accurate measurement of the pelvis is indicated, nuclear magnetic resonance imaging (MRI) may be used. The advantage of MRI over x-ray or computed tomography (CT) for pelvic assessment is the lack of ionizing radiation exposure.

Indications

1. Clinical evidence or obstetric history suggestive of pelvic abnormalities.

2. A history of pelvic trauma.

It should always be questioned whether the results obtained by radiologic assessment will have sufficient influence on the patient’s management to make the investigation worthwhile.

PREPARATION FOR LABOR

Before actual labor begins, a number of physiologic preparatory events usually occur.

Lightening

Two or more weeks before labor, the fetal head in most primigravid women settles into the brim of the pelvis. In multigravida, this often does not occur until early in labor. Lightening may be noted by the mother as a flattening of the upper abdomen and an increased prominence of the lower abdomen.

False Labor

During the last 4 to 8 weeks of pregnancy, the uterus undergoes irregular contractions that normally are painless. Such contractions appear unpredictably and sporadically and can be rhythmic and of mild intensity. In the last month of pregnancy, these contractions may occur more frequently, sometimes every 10 to 20 minutes, and with greater intensity. These Braxton Hicks contractions are considered false labor in that they are not associated with progressive cervical dilation or effacement. They may serve a physiologic role in preparing the uterus and cervix for true labor.

Cervical Effacement

Before the onset of parturition, the cervix is frequently noted to soften as a result of increased water content and collagen lysis. Simultaneous effacement, or thinning of the cervix, occurs as it is taken up into the lower uterine segment (Figure 8-8B). Consequently, patients often present in early labor with a cervix that is already partially effaced. As a result of cervical effacement, the mucous plug within the cervical canal may be released. The onset of labor may thus be heralded by the passage of a small amount of blood-tinged mucus from the vagina (“bloody show”).

FIGURE 8-8 A: The absence of cervical effacement before labor. B: Cervix being progressively taken up into the lower segment of the uterus (about 50% effaced). C: Cervix fully taken up (i.e., cervix is completely effaced).

STAGES OF LABOR

There are four stages of labor, each of which is considered separately. These stages in actuality are definitions of progress during labor, delivery, and the puerperium.

The first stage is from the onset of true labor to complete dilation of the cervix. The second stage is from complete dilation of the cervix to the birth of the baby. The third stage is from the birth of the baby to delivery of the placenta. The fourth stage is from delivery of the placenta to stabilization of the patient’s condition, usually at about 6 hours postpartum.

First Stage of Labor

PHASES

The first stage of labor consists of two phases: a latent phase, during which cervical effacement and early dilation occur, and an active phase, during which more rapid cervical dilation occurs (Figure 8-9). Although cervical softening and early effacement may occur before labor, during the first stage of labor, the entire cervical length is retracted into the lower uterine segment.

FIGURE 8-9 Cervical dilation and descent of the fetal head during labor. The first descent curve represents a fetus with a floating presenting part at the onset of labor, whereas the second represents a fetus with the presenting part fixed in the pelvis before labor.

(Modified from Friedman EA: Labor: Evaluation and Management, 2nd ed. East Norwalk, CT, Appleton-Century-Crofts, 1978, p 41.)

LENGTH

The length of the first stage may vary in relation to parity; primiparous patients generally experience a longer first stage than do multiparous patients (Table 8-2). Because the latent phase may overlap considerably with the preparatory phase of labor, its duration is highly variable. It may also be influenced by other factors, such as sedation and stress. The active phase begins when the cervix is 3 to 4 cm dilated in the presence of regularly occurring uterine contractions. The minimal dilation during the active phase of the first stage is nearly the same for primiparous and multiparous women: 1 and 1.2 cm/hour, respectively. If progress is slower than this, evaluation for uterine dysfunction, fetal malposition, or cephalopelvic disproportion should be undertaken.

TABLE 8-2 CHARACTERISTICS OF NORMAL LABOR

Characteristic	Primipara	Multipara
Duration of first stage	6-18 hr	2-10 hr
Rate of cervical dilation during active phase	1 cm/hr	1.2 cm/hr
Duration of second stage	30 min to 3 hr	5-30 min
Duration of third stage	0-30 min	0-30 min

MEASUREMENT OF PROGRESS

During the first stage, the progress of labor may be measured in terms of cervical effacement, cervical dilation, and descent of the fetal head. The clinical pattern of the uterine contractions alone is not an adequate indication of progress. After completion of cervical dilation, the second stage commences. Thereafter, only the descent, flexion, and rotation of the presenting part are available to assess the progress of labor.

CLINICAL MANAGEMENT OF THE FIRST STAGE

Certain steps should be taken in the clinical management of the patient during the first stage of labor.

MATERNAL POSITION

The mother may ambulate provided that intermittent monitoring ensures fetal well-being and the presenting part is engaged in patients with ruptured membranes. If she is lying in bed, the lateral recumbent position should be encouraged to ensure perfusion of the uteroplacental unit.

ADMINISTRATION OF FLUIDS

Because of decreased gastric emptying during labor, oral fluids are best avoided. However, fasting results in the more rapid development of ketosis in pregnant women. Placement of a 16- to 18-gauge venous catheter is advisable during the active phase of labor. Recently, it has been shown that giving at least 125 mL/hour of 10% dextrose (D) in normal saline (NS), compared with 5% D/NS or just NS, results in significantly shorter laborsThus, this intravenous route is used to both hydrate the patient with crystalloids and provide calories during labor, to administer oxytocin after the delivery of the placenta, and for the treatment of any unanticipated emergencies.

INVESTIGATIONS

Every woman admitted in labor should have a hematocrit or hemoglobin measurement and a blood clot held in the event that a crossmatch is needed. Blood group, Rhesus (Rh) type, and an antibody screen should be done if these are not known. It is also important to know the hepatitis B status of the mother so that a pediatrician can be notified if the mother is positive. Additionally, a voided urine specimen should be checked for the presence of protein and glucose.

MATERNAL MONITORING

Maternal pulse rate, blood pressure, respiratory rate, and temperature should be recorded every 1 to 2 hours in normal labor and more frequently if indicated. Fluid balance, particularly urine output and intake, should be monitored carefully.

ANALGESIA

Adequate analgesia is important during the first stage of labor (see later in this chapter).

FETAL MONITORING

The fetal heart rate should be evaluated either by auscultation with a De Lee stethoscope, by external monitoring with Doppler equipment, or by internal monitoring with a fetal scalp electrode. In uncomplicated pregnancies, continuous electronic fetal monitoring is not necessary, as several studies have demonstrated that intermittent auscultation of the fetal heart rate, when performed in conjunction with a 1:1 nurse-to-patient ratio, results in comparable outcomes. In patients with no significant obstetric risk factors, the fetal heart rate should be auscultated or the electronic monitor tracing 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, the fetal heart rate should be auscultated or the electronic monitoring tracing evaluated at least every 15 minutes during the active phase of the first stage of labor (immediately following a uterine contraction), and at least every 5 minutes during the second stage.

UTERINE ACTIVITY

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 rateThis can be achieved electronically using either an external tocodynamometer or an internal pressure catheter in the amniotic cavity. The latter is particularly of value when a patient’s labor is being augmented with oxytocin (Pitocin).

VAGINAL EXAMINATION

During the latent phase, particularly when the membranes are ruptured, vaginal examinations should be done sparingly to decrease the risk for an intrauterine infection. In the active phase, the cervix should be assessed about every 2 hours to determine the progress of labor. Cervical effacement and dilation, the station and position of the presenting part, and the presence of molding or caput in vertex presentations should be recorded.

AMNIOTOMY

The artificial rupture of fetal membranes may provide information on the volume of amniotic fluid and the presence or absence of meconium. In addition, rupture of the membranes may cause an increase in uterine contractility. Amniotomy incurs risks for chorioamnionitis if labor is prolonged and for umbilical cord compression or cord prolapse if the presenting part is not engaged.

Second Stage of Labor

At the beginning of the second stage, the mother usually has a desire to bear down with each contractionThis abdominal pressure, together with the uterine contractile force, combines to expel the fetus. During the second stage of labor, fetal descent must be monitored carefully to evaluate the progress of labor. Descent is measured in terms of progress of the presenting part through the birth canal.

In cephalic presentations, 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 a result of the compressive forces exerted by the bony maternal pelvis. Some molding is necessary for delivery under normal circumstances. If cephalopelvic disproportion is present, the amount of molding will be more pronounced. Caput is a localized, edematous swelling of the scalp caused by pressure of the cervix on the presenting portion of the fetal head. The development of both molding and caput can create a false impression of fetal descent.

The second stage generally takes from 30 minutes to 3 hours in primigravid women and from 5 to 30 minutes in multigravida.

MECHANISM OF LABOR

Six movements of the baby enable it to adapt to the maternal pelvis: descent, flexion, internal rotation, extension, external rotation, and expulsion (Figure 8-10). These movements are discussed here for both an occipitoanterior and occipitoposterior position at engagement. The mechanism of labor for other presentations is discussed in Chapter 13.

FIGURE 8-10 Mechanism of labor for a vertex presentation in the left occipitotransverse position. A: Flexion and descent. B and C: Continued descent and commencement of internal rotation. D: Completion of internal rotation to the occipitoanterior position followed by delivery of the head by extension.

DESCENT

Descent is brought about by the force of the uterine contractions, maternal bearing-down (Valsalva) efforts, and, if the patient is upright, gravity.

FLEXION

Partial flexion exists before labor as a result of the natural muscle tone of the fetus. During descent, resistance from the cervix, walls of the pelvis, and pelvic floor cause further flexion of the cervical spine, with the baby’s chin approaching its chest. In the occipitoanterior position, the effect of flexion is to change the presenting diameter from the occipitofrontal to the smaller suboccipitobregmatic (see Figure 8-2). In the occipitoposterior position, complete flexion may not occur, resulting in a larger presenting diameter, which may contribute to a longer labor.

INTERNAL ROTATION

In the occipitoanterior positions, the fetal head, which enters the pelvis in a transverse or oblique diameter, rotates so that the occiput turns anteriorly toward the symphysis pubis. Internal rotation probably occurs as the fetal head meets the muscular sling of the pelvic floor. It is often not accomplished until the presenting part has reached the level of the ischial spines (zero station) and therefore is engaged. In the occipitoposterior positions, the fetal head may rotate posteriorly, so the occiput turns toward the hollow of the sacrum.

EXTENSION

The flexed head in an occipitoanterior position continues to descend within the pelvis. 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 bulging of the perineum followed by crowning. Crowning occurs when the largest diameter of the fetal head is encircled by the vulvar ring. At this time, the vertex has reached station +5. When necessary, an incision in the perineum (episiotomy) may aid in reducing perineal resistance, although current management is to allow the fetus to deliver without an episiotomyThe head is born by rapid extension as the occiput, sinciput, nose, mouth, and chin pass over the perineum.

In the occipitoposterior position, the head is born by a combination of flexion and extension. At the time of crowning, the posterior bony pelvis and the muscular sling encourage further flexion. The forehead, sinciput, and occiput are born as the fetal chin approaches the chest. Subsequently, the occiput falls back as the head extends, and the nose, mouth, and chin are born.

EXTERNAL ROTATION

In both the occipitoanterior and occipitoposterior positions, the delivered head now returns to its original position at the time of engagement to align itself with the fetal back and shoulders. Further head rotation may occur as the shoulders undergo an internal rotation to align themselves anteroposteriorly within the pelvis.

EXPULSION

Following external rotation of the head, the anterior shoulder delivers under the symphysis pubis, followed by the posterior shoulder over the perineal body and the body of the child.

CLINICAL MANAGEMENT OF THE SECOND STAGE

As in the first stage, certain steps should be taken in the clinical management of the second stage of labor.

MATERNAL POSITION

With the exception of avoiding the supine position, the mother may assume any comfortable position for effective bearing down.

BEARING DOWN

With each contraction, the mother should be encouraged to hold her breath and bear down with expulsive efforts. This is particularly important for patients with regional anesthesia because their reflex sensations may be impaired.

FETAL MONITORING

During the second stage, the fetal heart rate should be monitored continuously or evaluated every 5 minutes in patients with obstetric risk factors. Fetal heart rate decelerations (head compression or cord compression) with recovery following the uterine contraction may occur normally during this stage.

VAGINAL EXAMINATION

Progress should be recorded about every 30 minutes during the second stage. Particular attention should be paid to the descent and flexion of the presenting part, the extent of internal rotation, and the development of molding or caput. During the second stage of labor, the retracted cervix is no longer palpable.

DELIVERY OF THE FETUS

When delivery is imminent, the patient is usually placed in the lithotomy position, and the skin over the lower abdomen, vulva, anus, and upper thighs is cleansed with an antiseptic solution. Uncomplicated deliveries, particularly in multiparous women, may be carried out in the supine position with the thighs flexed. The left lateral position may be used to deliver patients with hip or knee joint deformities that prevent adequate flexion, or for patients with a superficial or deep venous thrombosis in one of the lower extremities.

As the perineum becomes flattened by the crowning head, an episiotomy may be performed to prevent perineal lacerations. The performance of episiotomies may result in a higher proportion of lacerations that involve the anal sphincter (third degree) or anal mucosa (fourth degree). Although these more extensive lacerations may be surgically repaired, there is an increasing awareness of the occasional complication of anal incontinence of gas or feces following vaginal delivery.

To facilitate delivery of the fetal head, a Ritgen maneuver may be performed (Figure 8-11). The right hand, draped with a towel, exerts upward pressure through the distended perineal body, first to the supraorbital ridges and then to the chin. This upward pressure, which increases extension of the head and prevents it from slipping back between contractions, is counteracted by downward pressure on the occiput with the left hand. A recent (2008) randomized trial from Sweden found simple manual perineal support to be equally effective.

FIGURE 8-11 Ritgen’s maneuver. The fingers of the right hand, pressing posterior to the rectum, are used to extend the head while counterpressure is applied to the occiput by the left hand to allow for a more controlled delivery of the fetal head. Simple manual support of the perineum using one or both hands may be equally effective.

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 and then the nares are cleared. Suction of the nares is not performed if fetal distress or meconium-stained liquor is present because it may result in gasping and aspiration of pharyngeal contents. A second towel is used to wipe secretions from the face and head.

After the airway has been 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.

Following delivery of the head, the shoulders descend and rotate into the anteroposterior diameter of the pelvis and are delivered (Figure 8-12). Delivery of the anterior shoulder is aided by gentle downward traction on the externally rotated head. The brachial plexus may be injured if excessive force is used. The posterior shoulder is delivered by elevating the head. Finally, the body is slowly extracted by traction on the shoulders.

FIGURE 8-12 Delivery of the shoulders. A: Gentle downward traction on the head is applied to deliver the anterior shoulder. B: Gentle upward traction is used to deliver the posterior shoulder.

After delivery, blood will be infused from the placenta into the newborn if the baby is held below the mother’s introitus. Usually, the cord is clamped and cut within 15 to 20 seconds. Delayed cord clamping can result in neonatal hyperbilirubinemia as additional blood is transferred from the placenta to the newborn infant. The newborn is then placed under an infant warmer.

Third Stage of Labor

Immediately after the baby’s delivery, the cervix and vagina should be thoroughly inspected for lacerations and surgical repair performed if necessary. The cervix, vagina, and perineum may be more readily examined before the separation of the placenta because no uterine bleeding should be present to obscure visualization.

DELIVERY OF THE PLACENTA

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 as follows: (1) a fresh show of blood 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. Only when these signs have appeared should the assistant attempt traction on the cord. With gentle traction and counterpressure between the symphysis and fundus to prevent descent of the uterus into the pelvis, the placenta is delivered.

Following delivery of the placenta, attention should be paid to any uterine bleeding that may originate from the placental implantation site. Uterine contractions, which reduce this bleeding, may be hastened by uterine massage and the use of oxytocinIt is routine to add 20 U of oxytocin to the intravenous infusion after the baby has been deliveredThe placenta should be examined to ensure its complete removal and to detect placental abnormalities. If the patient is at risk for postpartum hemorrhage (e.g., because of anemia, prolonged oxytocic augmentation of labor, multiple gestation, or hydramnios), manual removal of the placenta, manual exploration of the uterus, or both may be necessary.

PERINEAL LACERATIONS

Perineal lacerations, with or without episiotomy, may be classified as follows:

• First degree: A laceration involving the vaginal epithelium or perineal skin

• Second degree: A laceration extending into the subepithelial tissues of the vagina or perineum with or without involvement of the muscles of the perineal body

• Third degree: A laceration involving the anal sphincter

• Fourth degree: A laceration involving the rectal mucosa

If an episiotomy has been performed (Figure 8-13),it should be repaired as illustrated in Figure 8-14Absorbable sutures (00) should be used, and a rectal examination should ensure that the sutures have not inadvertently transected the rectal mucosa. A third-degree tear (Figure 8-15) should be repaired as shown in Figure 8-16.

FIGURE 8-13 A: Mediolateral episiotomy. B: Midline episiotomy.

FIGURE 8-14 A: Repair of a midline episiotomy. A taped sponge is placed in the upper vagina, and a continuous locked 00 or 000 absorbable suture closes the vaginal epithelium from the apex to the hymeneal ring. B: Three interrupted sutures are used to close the deep perineal fascia (of Colles) and underlying levator ani muscles. The vaginal epithelial suture is brought below the skin into the subcutaneous tissue. C: The same continuous suture is used to close the superficial fascia down to the anal edge of the episiotomy. D: The same suture is used as a subcuticular stitch coming back to the hymeneal ring, where it is doubly tied. The sponge is then removed. (This is very important.)

FIGURE 8-15 Third-degree perineal tear extending into the rectum and avulsing the circular rectal sphincter.

FIGURE 8-16 Repair of a third-degree tear involves approximating the fascia surrounding the rectal sphincter muscle and reapproximating the vaginal tears with locked continuous sutures. The process is then completed as with a midline episiotomy repair.

Fourth Stage of Labor

The hour immediately following delivery requires close observation of the patient. Blood pressure, pulse rate, and uterine blood loss must be monitored closely. It is during this time that postpartum hemorrhage commonly occurs, usually because of uterine relaxation, retained placental fragments, or unrepaired lacerations. Occult bleeding (e.g., vaginal hematoma formation) may manifest as pelvic pain. An increase in pulse rate, often out of proportion to any decrease in blood pressure, may indicate hypovolemia.

Induction and Augmentation of Labor

Induction of labor is the process whereby labor is initiated by artificial means; augmentation is the artificial stimulation of labor that has begun spontaneously.

In the absence of the natural onset of labor, pharmacologic methods may be used to initiate labor. However, labor should be induced only after appropriate assessment of the mother and fetus and an explanation to the patient of the indications for induction. In the absence of a medical indication for labor induction, fetal maturity should be confirmed by either appropriate pregnancy dating, ultrasonic measurements, or amniotic fluid analysis (e.g., lecithin/sphingomyelin [L/S] ratio).

Cervical effacement and softening (ripening) occur before the onset of spontaneous labor. Cervical ripening frequently does not occur before a decision about labor induction, yet the success of induction is dependent on these necessary changes in the cervix.

Several mechanical and pharmacologic approaches promote cervical ripening before the actual induction of uterine contractions. Local application of prostaglandins may be used. Currently approved pharmacologic treatments include intravaginal application of prostaglandin E₂ using a vaginal insert called Cervidil (on a string), which can be removed quickly if the medication causes hyperstimulation. Cytotec, a synthetic prostaglandin E₁ analogue, has been approved for cervical ripening. One 25-μg tablet placed intravaginally effectively initiates cervical ripening. Although prostaglandin administration has been demonstrated to shorten the duration of labor induction, the impact on cesarean birth rates due to failed induction has been minimal.

Other methods of cervical ripening may include intrauterine placement of catheters or the use of osmotic dilators (see Figure 26-4). Manual separation of the chorioamnion from the lower uterine segment does not necessarily speed the onset of labor. Although controversial, artificial rupture of the membranes may be used to increase uterine activity, and perhaps to speed cervical change, when performed in conjunction with administration of oxytocin.

In addition to cervical ripening, induction of labor requires the initiation of effective uterine contractions. Oxytocin is identical to the natural pituitary peptide, and it is the only drug approved for induction and augmentation of labor. Pitocin is the synthetic preparation. The physician must be fully aware of the indications and the contraindications for the use of oxytocin (Table 8-3). In general, induction of labor before term is indicated only when the continuation of pregnancy represents a significant risk to the fetus or mother. In some situations, induction may be indicated at term, as in the case of premature rupture of the membranes. Induction at term for convenience is not appropriate unless the patient has a history of previous precipitous delivery (less than 3 hours) or lives an unusually long distance from the hospital.

TABLE 8-3 INDICATIONS AND CONTRAINDICATIONS FOR INDUCTION AND AUGMENTATION OF LABOR

Induction	Augmentation
INDICATIONS
*Maternal*
Preeclampsia Diabetes mellitus Heart disease Prolonged pregnancy Intrauterine growth restriction (IUGR)

Abnormal labor (in the presence of inadequate uterine activity)

Prolonged latent phase

Prolonged active phase

Fetoplacental

Abnormal fetal testing

Rh incompatibility

Fetal abnormality

Premature rupture of membranes (PROM)

Chorioamnionitis

CONTRAINDICATIONS Maternal Absolute Contracted pelvis Same contraindications as for maternal and fetoplacental Relative Prior uterine surgery Classic cesarean birth Complete transection of uterus (myomectomy, reconstruction) Overdistended uterus Fetoplacental Preterm fetus without lung maturity Acute fetal distress Abnormal presentation

In general, any condition that makes normal labor dangerous for the mother or fetus is a contraindication to induction or augmentation of labor. The most common contraindication has been prior uterine surgery in which there has been complete transection of the uterine wall. However, a previous lower transverse incision is no longer considered a contraindication to a trial of labor. This is referred to as vaginal birth after cesarean (VBAC).

Induction of labor before term for maternal or fetal indications must not be undertaken without the assessment of fetal pulmonary maturity, provided that a delay will not jeopardize the mother or fetus. Fetal lung maturity can most often be accelerated within 24 to 48 hours by the use of glucocorticoids.

TECHNIQUE FOR INDUCTION AND AUGMENTATION OF LABOR

A hospital obstetric service must establish guidelines for the proper use of oxytocin for induction and augmentation of labor. In general, an assessment and plan of management must be outlined in the patient’s medical record. Indications for induction of labor should be clearly stated. It is helpful to assess the likelihood of success by a careful pelvic examination to determine the Bishop score, which evaluates the status of the cervix and the station of the fetal head (Table 8-4). A high score (9 to 13) is associated with a high likelihood of a vaginal delivery, whereas a low score (<5) is associated with a decreased likelihood of success (65% to 80%). Before induction is begun, the patient’s blood must be typed and screened for antibodies. A blood specimen should be held in the laboratory in case crossmatching becomes necessary. Continuous electronic monitoring of the fetal heart rate and uterine activity is required during induction. An internal uterine catheter for monitoring uterine pressure is suggested if intensity cannot be adequately assessed.

TABLE 8-4 BISHOP SCORE TO ASSESS LIKELIHOOD OF SUCCESSFUL INDUCTION OF LABOR

Oxytocin Infusion

Several principles should be followed when oxytocin is used to induce or augment labor:

1. Oxytocin must be given intravenously to allow it to be discontinued quickly if a complication such as uterine hypertonus or fetal distress develops. Because oxytocin has a half-life of 3 to 5 minutes, its physiologic effect will diminish quickly (within 15 to 30 minutes) after discontinuation.

2. A dilute infusion must be used and “piggybacked” into the main intravenous line so that it can be stopped quickly if necessary, without interrupting the main intravenous route.

3. The drug is best infused with a calibrated infusion pump that can be easily adjusted to effect the required infusion rate accurately.

4. The induction of labor for a specific indication generally should not exceed 72 hours. In patients with a low Bishop score, it is not unusual for an induction to progress slowly. If the cervix effaces and dilates, it is recommended that the membranes be ruptured on the third day. If adequate progress is not made within 12 hours of rupturing the membranes, a cesarean delivery may be performed.

5. If adequate labor is established, the infusion rate and the concentration may be reduced, especially during the second stage of labor. This principle avoids the risks of hyperstimulation and fetal distress, which frequently occur once labor has been established.

Substantial variation exists regarding the initial dose, incremental dose, and time interval between dose increments when oxytocin is used for labor induction and augmentation. Well-performed clinical studies have supported both low-dose (1 to 30 mU/min) and high-dose (4 to 40 mU/min) protocols, as seen in Table 8-5It is not surprising that many protocols use “moderate” doses of oxytocin. Generally, intervals between dose increments should be no less than 20 minutes to permit time for steady-state plasma levels of oxytocin to be achieved and to prevent an increased risk for uterine hyperstimulation.

TABLE 8-5 METHOD OF OXYTOCIN INFUSION FOR INDUCTION OR AUGMENTATION

SOLUTION
10 units of oxytocin in 1000 mL of 5% dextrose or balanced salt solution (10 mU/mL)
ADMINISTRATION
Piggyback into main IV line; administer solution by infusion pump
	Low-Dose Protocol	High-Dose Protocol
Starting dose	1 mU/min	4 mU/min
Increment	1 mU/min	4 mU/min
Interval	20 min	20 min
Limited by	5 contractions in 10 min	7 contractions in 15 min
Maximal dose	20-30 mU/min	40 mU/min

COMPLICATIONS

The use of oxytocin for the induction and augmentation of labor can cause three major complications. First, an excessive infusion rate can cause hyperstimulation and thereby cause fetal distress from ischemia. In rare situations, a tetanic contraction can occur and lead to rupture of the uterus. Second, because oxytocin has a similar structure to antidiuretic hormone, it has an intrinsic antidiuretic effect and will increase water reabsorption from the glomerular filtrate. Severe water intoxication with convulsions and coma can occur rarely when oxytocin is infused continuously for more than 24 hours. Third, prolonged infusion of oxytocin can result in uterine muscle fatigue (nonresponsiveness) and postdelivery uterine atony (hypotonus), which can increase the risk for postpartum hemorrhage.

Puerperium

The puerperium consists of the period following delivery of the baby and placenta to about 6 weeks postpartum. During the puerperium, the reproductive organs and maternal physiology return toward the prepregnancy state, although menses may not return for much longer.

ANATOMIC AND PHYSIOLOGIC CHANGES

Involution of the Uterus

Through a process of tissue catabolism, the uterus rapidly decreases in weight from about 1000 g at delivery to 100 to 200 g at about 3 weeks postpartum. The cervix similarly loses its elasticity and regains its prepregnancy firmness. For the first few days after delivery, the uterine discharge (lochia) appears red (lochia rubra), owing to the presence of erythrocytes. After 3 to 4 days, the lochia becomes paler (lochia serosa), and by the 10th day, it assumes a white or yellow-white color (lochia alba). Foul-smelling lochia suggests endometritis.

Vagina

Although the vagina may never return to its prepregnancy state, the supportive tissues of the pelvic floor gradually regain their former tone. Women who deliver vaginally should be taught and encouraged to perform Kegel exercises (intermittent tightening of the perineal muscles) to maintain and improve the supportive tissues of the pelvic floor.

Cardiovascular System

Immediately after delivery, there is a marked increase in peripheral vascular resistance due to the removal of the low-pressure uteroplacental circulatory shunt. The cardiac output and plasma volume gradually return to normal during the first 2 weeks of the puerperium. As a result of the loss of plasma volume and the diuresis of extracellular fluid, a marked weight loss occurs in the first week.

Psychosocial Changes

It is fairly common for women to exhibit a mild degree of depression a few days after delivery. The “postpartum blues” are probably due to both emotional and hormonal factors. With understanding and reassurance from both family and physician, this usually resolves without consequence. Any prolonged episodes of depression during or after pregnancy should receive urgent attention.

Return of Menstruation and Ovulation

In women who do not nurse, menstrual flow usually returns by 6 to 8 weeks, although this is highly variable. Although ovulation may not occur for several months, particularly in nursing mothers, contraceptive counseling and use should be emphasized during the puerperium to avoid an undesired pregnancy.

Breastfeeding

There are many advantages to breastfeeding. First, breast milk is the ideal food for the newborn, is inexpensive, and is usually in good supply. Second, breastfeeding accelerates the involution of the uterus because suckling stimulates the release of oxytocin, thereby causing increased uterine contractions. Third, and probably most important, there are immunologic advantages for the baby from breastfeeding. Various types of maternal antibodies are present in breast milk. The predominant immunoglobulin is secretory immunoglobulin A (IgA), which provides protection in the infant’s gut by preventing attachment of harmful bacteria (e.g., Escherichia coli) to cells on the mucosal surface. This prevents the bacteria from penetrating the bowel wall. It is also thought that maternal lymphocytes pass through the infant’s gut wall and initiate immunologic processes that are not yet well understood. Breastfeeding thereby provides the newborn with passive immunity against certain infectious diseases until its own immune mechanisms become fully functional by 3 to 4 months.

LACTATION

Various hormones, such as estrogen, progesterone, human chorionic gonadotropin, cortisol, insulin, prolactin, and placental lactogen, play an important role in preparing the breasts for lactation. At delivery, two events are instrumental in initiating lactation. First is the drop in placental hormones, particularly estrogen. Before delivery, these hormones interfere with the lactogenic action of prolactin. Second, suckling stimulates the release of prolactin and oxytocin. The latter causes contraction of the myoepithelial cells in the alveoli and milk ducts. The suckling stimulus is thought to be important for milk production, as well as for the ejection of colostrum and milk.

On about the second day after delivery, colostrum is secreted. Its content is composed mostly of protein, fat, and minerals. It is the colostrum that contains secretory IgA. After about 3 to 6 days, the colostrum is replaced by mature milk. The content of milk varies considerably depending on the nutritional status of the mother and the gestational age at the time of delivery. In general, the major components of breast milk are proteins, lactose, water, and fat. The major proteins synthesized in the human breast, which are unique and are not found in cows’ milk, are casein, lactalbumin, and ß-lactoglobulin. Essential amino acids are delivered from the mother’s blood, and some of the nonessential amino acids can be synthesized in the breast. In addition, breast milk is a source of omega-3 fatty acids, which are important for early brain development.

LACTATION SUPPRESSION

When the mother chooses not to breastfeed, lactation suppression is indicated. The simplest, and probably safest, method to accomplish this is to use a tight-fitting bra. If breast distention does occur, pumping only makes the situation worse. Ice packs should be applied and the discomfort managed with analgesics.

COMPLICATIONS OF BREASTFEEDING

Cracked Nipples

If the nipples of the breast become fissured, nursing may become difficult. Because fissures are also a portal of entry for bacteria, they should be managed aggressively with a nipple shield and an appropriate cream, such as lanolin or Masse breast cream. Further breastfeeding should be temporarily stopped. Milk can be expressed manually until the nipples heal, at which time breastfeeding can be resumed.

Mastitis

This is an uncommon complication of breastfeeding and usually develops after 2 to 4 weeks. 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 culture and sensitivity, and the mother should be started on a regimen of antibiotics immediately. Because most staphylococcal organisms are penicillinase producing, a penicillinase-resistant antibiotic, such as dicloxacillin, should be used. Breastfeeding may be discontinued but is not contraindicated. 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 if nursing is discontinued.

Drug Passage to the Newborn

Because an infant may ingest up to 500 mL of breast milk per day, maternally administered drugs that pass into breast milk may have a significant effect on the infant. The amount of drug found in breast milk depends on the maternal dose, the rate of maternal clearance, the physicochemical properties of the drug, and the composition of the breast milk with respect to fat and protein. The gestational age of the infant may also be a determinant of the ultimate drug effect. Table 8-6 lists selected drugs with their reported newborn effects.

TABLE 8-6 EFFECTS OF MATERNAL DRUG INGESTION ON BREASTFEEDING INFANTS

Drug	Reported Infant Effects
SEDATIVE-HYPNOTICS
Diazepam	Sedation
ANTIPSYCHOTICS
Chlorpromazine	No adverse effects reported
Haloperidol	No adverse effects reported
NONNARCOTIC ANALGESICS
Acetaminophen	No adverse effects reported
Salicylates	Theoretical risk for platelet dysfunction
ANTICONVULSANTS^∗
Phenobarbital	Sedation
Phenytoin	Sedation, decreased sucking
NARCOTICS
Heroin	May cause addiction
Methadone	Infant death reported
Meperidine	No adverse effects reported
ANTIBIOTICS
Penicillin	May modify bowel flora, cause allergy, or interfere with sepsis work-up
Ampicillin	Same as for penicillin
Erythromycin	Same as for penicillin
Nitrofurantoin	Theoretical risk for hemolytic anemia in infants with glucose-6-phosphate dehydrogenase deficiency
Tetracycline	Same as for penicillin; theoretical risk for discoloration of teeth and inhibition of bone growth
DIGOXIN	No adverse effects reported
THYROID DRUGS
Thyroxine	May interfere with screening for hypothyroidism
Propylthiouracil	Nodular goiter
ANTIHYPERTENSIVES
Methyldopa	No adverse effects reported
Propranolol	No adverse effects reported
THEOPHYLLINE	One case of infant irritability following maternal administration of a rapidly absorbed oral preparation

∗ See Chapters 7 and 16.

Interconception Care

Women who have poor pregnancy outcomes, such as preterm births and perinatal deaths, are at greater risk for having the same problems with subsequent pregnancies. Programs are now offering comprehensive interconception care to address conditions that have been shown to cause poor outcomes with interventions that could mitigate or eliminate any recurrence. The rationale for this approach is to provide continuous obstetric care rather than episodic care triggered by another pregnancy. Studies are underway to determine the value of these programs.

Obstetric Analgesia and Anesthesia

The goal of obstetric analgesia and anesthesia is to provide effective pain relief for the mother during the course of labor and delivery that is safe for her and her baby and that has minimal or no adverse effects on the progress and outcome of labor. Anesthetic practices have evolved to include an increased reliance on highly effective and safe regional anesthetic techniques, using low-concentration combinations of narcotics and local anesthetics in order to minimize the adverse effects of each. Maternal anesthetic risk has also declined owing to the increased awareness of the safety benefits of regional over general anesthesia for cesarean birth. Maternal mortality due to anesthesia has decreased to less than 1 in 500,000 mothers.

UTERINE BLOOD FLOW

Uterine blood flow at term accounts for 700 to 900 mL/min (about 12% of maternal cardiac output) and is not autoregulated. Regional analgesia or anesthesia may increase uterine blood flow, especially in preeclamptic patients, by relieving pain and stress and reducing circulating catecholamines. Regional analgesia or anesthesia may also decrease uterine blood flow if hypotension occurs and is not properly and promptly treated. Adequate hydration (e.g., 1000 mL of lactated Ringer’s), 30 to 60 minutes before regional anesthesia, helps improve uterine blood flow and mitigates the risk for hypotension. If hypotension does occur (>15% below baseline, or <100 mm Hg systolic blood pressure), a vasopressor (e.g., ephedrine, 10 mg given intravenously) will typically restore maternal blood pressure and uterine blood flow.

PAIN PATHWAYS

The pain pathways of parturition are shown in Figure 8-17.

FIGURE 8-17 Pain pathways of parturition. T10 to L1 supply innervation to the uterus, L1 to S4 supply pain pathways to the vagina and deep pelvic structures, S2 to S4 supply nerve fibers to the pudendal nerve.

ADVERSE EFFECTS OF LABOR PAIN

Maternal hyperventilation during contractions causes respiratory alkalosis that results in (1) a shift of the oxyhemoglobin dissociation curve to the left, (2) increased affinity of maternal hemoglobin for oxygen, and (3) decreased oxygen offloading to the fetus. The cyclical nature of contraction pain may cause a hyperventilation-hypoventilation syndrome whereby the mother blows off so much carbon dioxide during a contraction that she hypoventilates between contractions and may even become mildly hypoxemic between contractions. This syndrome is exacerbated by systemic narcotics because they do not adequately relieve the pain of the contraction but add to the respiratory depression between contractions. Hypoxemia between contractions may be attenuated by providing supplemental oxygen. Finally, labor pain results in increased levels of circulating catecholaminesThe α-adrenergic effects of the catecholamines may reduce uterine blood flow, whereas the β₂-adrenergic effects may impair uterine contractility.

OPTIONS FOR LABOR PAIN RELIEF

Nonpharmacologic methods include education and psychoprophylaxis (Lamaze method), emotional support, back massage, hydrotherapy, biofeedback, transcutaneous electrical nerve stimulation (TENS), acupuncture, and hypnosis (hypnobirthing). Scientific assessment of these methods has yielded inconsistent results. Acupuncture decreases pain in most studiesThese techniques tend to work best early in the first stage of labor when the pain is least intense and may decrease pharmacologic use at that time.

Pharmacologic treatment options include parenteral narcotics, regional analgesia (epidural, spinal, combined spinal-epidural, paracervical, caudal, and pudendal nerve blocks), and inhalational analgesia.

Parenteral narcotics have very limited efficacy for the relief of labor pain. They work best in the early first stage when the pain is primarily visceral and less intense. All opioids readily cross the placental barrier and may cause neonatal respiratory depression depending on the dose and timing relative to delivery. They may also cause decreased fetal heart rate variability (not necessarily due to fetal acidosis) and impair neonatal breastfeeding. Fentanyl and nalbuphine have the shortest neonatal half-lives of the commonly used parenteral narcotics.

Neuraxial analgesia (medication injected into the spinal column) is undoubtedly the most effective form of labor pain relief. Lumbar epidural analgesia is the most common form of neuraxial analgesia used to treat labor pain, and its use has been steadily increasing to 60% nationally. It may be used to provide pain relief for the first and second stages of labor, and, by injecting a higher concentration of local anesthetic, the block may be intensified and extended to provide surgical anesthesia for cesarean delivery or postpartum tubal ligation. There is no fixed cervical dilation at which it is appropriate to provide epidural analgesia as long as the patient is having regular, painful contractions. Modern epidural management includes an initial bolus of local anesthetic (bupivacaine, ropivacaine, or lidocaine) and narcotic (fentanyl or sufentanil) to achieve a T10 sensory level, followed by an infusion of a dilute solution of the same agents until delivery. Pain during the first stage of labor is conducted along the sympathetic fibers, entering the spinal cord between T10 and L2. Dilute solutions can be used that permit ambulation, or the “walking epidural.” The goal is to avoid motor block to minimize any adverse effects on maternal expulsive efforts in the second stage.

A pudendal nerve block anesthetizes somatic afferent nerve fibers entering the spinal cord at sacral segments S2 to S4. It is usually effective at relieving the perineal pain of the second stage of labor, along with the pain of episiotomy and episiotomy repair. It does not affect the ongoing pain of uterine contractions.

ANESTHESIA FOR CESAREAN DELIVERY

The type of anesthesia selected for cesarean delivery is determined by the urgency of the surgery, the presence or absence of a preexisting epidural catheter for labor, and the patient’s medical condition, pregnancy-related complications, and presence of any contraindications to regional anesthesia. Absolute and relative contraindications to regional anesthesia are listed in Box 8-1All patients requiring anesthesia for surgery must have an airway examination regardless of how urgent the surgery is. A brief history must also be elicited. If the history or the physical examination suggests that the intubation will be difficult (Box 8-2), the patient must have a regional anesthetic or an awake intubation, or the operation must be started under local anesthesia.

BOX 8-2 Factors Suggesting Difficult Intubation.

• Obesity, short neck

• Neck flexion-extension limitations at atlanto-occipital joint

• Short chin-hyoid distance (receding chin)

• Limited mouth opening

• Poor dentition, buck teeth

• Excess oropharyngeal tissues (want to see uvula and tonsillar pillars)

• Large tongue

All patients are premedicated with a nonparticulate antacid. Routine monitors are placed, including noninvasive blood pressure monitors, electrocardiograph, and pulse oximeter, and adequate left uterine displacement must be instituted. Supplemental oxygen is provided. A crystalloid preload (bolus over 30 to 60 minutes) of 10 to 15 mL/kg is given before regional anesthesia.

For elective or urgent cesarean delivery (nonemergency), regional anesthesia is preferred because the airway is maintainedComplications involving loss of the airway are the leading causes of anesthetic-related maternal mortality and are usually associated with general anesthesia. General anesthesia carries a 16-fold higher risk of anesthesia-related maternal mortality compared with regional anesthesia (Table 8-7). Parturients have a higher risk for airway complications than nonpregnant patients because they have (1) an 8 times higher chance of failed intubation, (2) a 60% increased oxygen consumption, (3) a decreased functional residual capacity (FRC) resulting in a lower oxygen store, and (4) an increased risk for aspiration.

TABLE 8-7 CAUSES OF ANESTHETIC-RELATED MATERNAL DEATHS IN THE UNITED STATES, 1979-1990

Causes	Anesthesia Deaths (%)
Airway problems
Aspiration	23
Induction, intubation problems	12
Inadequate ventilation	12
Respiratory failure	2
Local anesthetic toxicity	13
High spinal, epidural	9
Cardiac arrest	23
Overdosage	1
Anaphylaxis	1

If no epidural is in place, a spinal block is frequently used. A comparison of the characteristics of spinal and epidural anesthesia is shown in Table 8-8.

TABLE 8-8 COMPARISON OF SPINAL AND EPIDURAL ANESTHESIA

Spinal	Epidural
ADVANTAGES
Faster	Can tailor duration to need
Technically easier	Lower chance of postdural puncture headache
More reliable	Slower onset
Defined end point	Beneficial in patients with cardiac and hypertensive disorders
Minimal chance of patchy block	Faster offset Discharge to room sooner

Denser block Lower drug exposure for mother and fetus No chance of systemic toxicity DISADVANTAGES Defined (limited) duration Slower onset Higher chance of postdural puncture headache (limited by use of small-bore, pencil-point needles)

Higher risk for systemic toxicity due to accidental intravenous injection

Risk for high spinal due to inadvertent intrathecal or subdural injection

Risk for “patchy block” due to inadequate or asymmetrical dermatomal spread

General anesthesia is employed for cesarean delivery in three situations: (1) there is extreme urgency without a preexisting, functional epidural catheter; (2) there is a contraindication to regional anesthesia; or (3) regional anesthesia has failed. When a relative contraindication to regional anesthesia is present, the benefits of regional anesthesia frequently outweigh the risks in the pregnant patient.

The protocol for general anesthesia for cesarean birth includes oral administration of nonparticulate antacid (sodium citrate), routine monitoring and left uterine displacement, preoxygenation for at least four vital capacity breaths, and rapid sequence induction of anesthesia with cricoid pressure followed by intubation to prevent regurgitation and pulmonary aspiration of gastric contentsOnce the correct position of the endotracheal tube has been confirmed by end-tidal CO₂ and auscultation of the lungs, surgery may begin.

Induction agents for general anesthesia include propofol (most commonly), thiopental, etomidate (when cardiovascular stability is particularly desired), and ketamine (for hypovolemic or asthmatic patients). The muscle relaxant used to facilitate intubation is succinylcholine (unless contraindicated), owing to its rapid onset and brief duration of action. If contraindicated, vecuronium or rocuronium may be used. Oxygen delivery is maintained at 50% to 100% until delivery if the baby is stressed. Nitrous oxide may be added. After induction, a potent inhalational agent is administered and at a modest level (0.5 minimum alveolar concentration [MAC]) to minimize myometrial relaxation. Narcotics may be administered after the delivery of the baby to reduce the need for inhalational anesthesia and provide postoperative pain relief. The patient must be extubated only when fully awake to minimize the risk for aspiration.

PATIENTS WHO BENEFIT FROM EARLY ANESTHETIC CONSULTATION

General anesthesia can usually be avoided if an epidural catheter is already in place, so it is helpful to identify those patients who are at increased risk for requiring surgery, and those patients who have a normal chance of needing surgery but would pose an especially high anesthetic risk. Patients who are at increased risk for emergency surgery may be advised to get a preemptive epidural catheter early to avoid the risks of a crash cesarean under general anesthesia (e.g., breech presentation, multiple gestation, prematurity, macrosomia, poor fetal heart rate tracing, severe preeclampsia, morbid obesity). These fetuses may also benefit from the improved uterine blood flow and controlled delivery that epidural analgesia allows.

Mothers who are at particularly high anesthetic risk should receive a prelabor consultation for significant preexisting medical conditions (e.g., difficult airway; see Box 8-2); significant respiratory, cardiac, or neurologic disease; spinal surgery; and suspected or known susceptibility to malignant hyperthermia.

Unintended Consequences of Regional Anesthesia or Analgesia

Patients who receive epidural analgesia for labor pain have a similar duration of the first stage of labor, but the second stage may be prolonged by 15 minutes on average. Theoretically, a prolongation of the second stage could arise from effects of the release of endogenous oxytocin, prostaglandin F_2a, and other hormones responsible for the propagation of labor. Prolongation of the second stage could also be due to impaired ability to push (unlikely as long as motor block is avoided by appropriate adjustment of the epidural infusion), or decreased maternal urge to push due to sensory blockade. The latter can usually be overcome by appropriate coaching and decreasing or halting the epidural infusion.

Other side effects and complications of regional anesthesia or analgesia include fever (0.5°C increased body temperature), headache, and backache. The association with maternal fever may be due to (1) an alteration in the thermoregulatory threshold, (2) interference with peripheral thermoreceptor input to the central nervous system, (3) shifting heat calories from the core to the periphery by vasodilation, or (4) an imbalance between maternal heat production and loss (decreased hyperventilation, decreased lower body sweating, increased shivering).

The risk for headache is about 1% to 2% with spinal anesthesia, and it is lower with an epidural (less than 1%). It occurs when there is an unintended dural puncture (“wet tap”). Postdural puncture headaches are self-limited, usually resolving within 5 to 7 days. Cerebrospinal fluid leaks through the hole in the dura, resulting in low intracranial pressure. The hallmark is a severe positional headache—little or no headache supine, sudden onset of severe headache when sitting upright or standing. The dural hole will heal in about 1 week or can be sealed with an epidural blood patch. Symptomatic treatment includes narcotics, nonsteroidal antiinflammatory drugs, caffeine, sumatriptan, and abdominal binder.

There appears to be no association between new-onset, long-term back pain and labor epidural analgesiaThe risk for new, chronic back pain in parturients is high (up to 47%) whether or not they have had an epidural.

Resuscitation of the Newborn

Improved surveillance using antenatal and intrapartum fetal heart rate monitoring, real-time ultrasonography, amniocentesis, and umbilical artery Doppler assessments has allowed the clinician to recognize the fetus at risk who may need special care at birth. The goals of an organized approach to neonatal resuscitation are to reverse any intrauterine hypoxia and to prevent postnatal asphyxia, which may result in acute major organ damage and lifelong handicaps.

Preparation for Extrauterine Life

Prematurity is the leading cause of poor neonatal outcome because the fetus has not yet progressed through complete stages of anatomic development and biochemical maturation. Even the fetus delivered at term undergoes changes before and with the onset of labor.

During pregnancy, fetal thyroxine (T₄) is converted to reverse triiodothyronine (rT₃), which is metabolically inactive. Several days before the onset of term labor, cortisol levels increase in the fetus and induce a change in thyroid hormone dynamics. Cortisol induces the enzyme system, allowing the conversion of T₄ to triiodothyronine (T₃), which is metabolically more active and necessary for neonatal thermogenesis. At birth, there is a surge of thyroid-stimulating hormone (TSH), and at no time during life does this hormone reach such high levels as it does 30 minutes after birth. This is followed by a hyperthyroid neonatal state for several days, which is necessary for the newborn to maintain its body temperature.

A second change that occurs with the onset of labor is a change in fetal breathing activity. Fetal breathing, as observed by real-time ultrasonography, is rarely observed once labor is established. This is thought to be associated with a decrease in pulmonary fluid dynamics that may be important for the onset of respiration after delivery and the retention of surfactant in the lungs.

Finally, labor is a stress to the fetus that stimulates the release of catecholamines. This may be responsible for the mobilization of glucose, lung fluid absorption, alterations in the perfusion of organ systems, and, possibly, the onset of respiration. Only at times of severe stress later in life are catecholamine levels as high as those at birth.

ETIOLOGY OF NEONATAL CARDIORESPIRATORY DEPRESSION

At term, 1% of infants require vigorous resuscitation (positive pressure ventilation for more than 1 minute). At earlier stages of gestation, almost all infants require some type of supportive care.

FACILITATING NEONATAL ADAPTATION

The physician performing the delivery should delegate the responsibility for neonatal resuscitation. All nurses working in the delivery room should be trained in techniques of neonatal assessment and resuscitation. If risk factors increase the likelihood of delivering a depressed infant, a pediatrician trained in neonatal resuscitation should be summoned.

Following delivery of a normal newborn, the following important steps should occur:

1 Clear the Airway

Descent through the birth canal causes compression of the chest wall, resulting in the discharge of fluid from the mouth and nose. When the head emerges from the vagina, the physician should use a towel to remove secretions from the face. In addition, a bulb suction may be used to aspirate secretions from the oropharynx. Initially, the bulb suction should not be used to suction the nose because nasal stimulation may initiate a gasp and cause bradycardia from a vagal reflex. If a moderate amount of meconium is present, placing a nasal tracheal catheter into the oropharynx and applying suction before delivering the body is thought to decrease the risk for meconium aspiration. If meconium is present and the baby is not vigorous (>100 heart rate, strong respiratory effort, and good muscle tone), intubation should be performed to suction the trachea after suction of the mouth.

2 Dry the Newborn

An important part of neonatal adaptation is the initiation of nonshivering thermogenesis. Excessive cooling from exposure of the wet skin is detrimental to all preterm infants and to depressed full-term infants. The newborn should be placed in a preheated environment, and the physician should dry off the infant with a towel before cutting the cord. This also serves to stimulate the onset of respiration.

3 Clamp the Cord

The umbilical arteries usually close spontaneously within 45 to 60 seconds of birth, whereas the umbilical vein remains patent for 3 to 5 minutes or longer. Delayed cord clamping significantly increases the neonatal blood volume, which increases the likelihood of neonatal jaundice and tachypnea. The ideal time for clamping the cord is 20 to 30 seconds after birth.

4 Ensure Onset of Respiration

The onset of respiration is normally within a few seconds of birth. If respiration has not commenced at 30 seconds of life or the heart rate is less than 100, positive pressure ventilation with oxygen should be started. If resuscitation is started with less than 100% oxygen and there is no improvement within 90 seconds of birth, oxygen should be increased to 100%.

5 Correct Surfactant Deficiency

For the premature infant, surfactant deficiency is the basic defect responsible for the development of the respiratory distress syndrome. Exogenous surfactant replacement varies from synthetic surfactant to modified or unmodified extracts of natural surfactant. These substances can be given by tracheal injection at birth to prevent the respiratory distress syndrome, or they can be given after the syndrome has developed to reduce its severity and prevent mortality.

Apgar Score

The Apgar score is an excellent tool for assessing the overall status of the newborn soon after birth (1 minute) and after a 5-minute period of observation (Table 8-9). A normal Apgar score is 7 or greater at 1 minute and 9 or 10 at 5 minutes.

TABLE 8-9 APGAR SCORE FOR DETERMINING CONDITION OF A NEWBORN INFANT

Resuscitation of the Asphyxiated Infant

During the past 15 years, increasing emphasis has been placed on transferring the mother with a high-risk pregnancy to a tertiary care regional center before labor, rather than transferring the sick neonate after delivery.

Ideally, at the time of delivery, a segment of cord should be doubly clamped to allow blood gas determinations on cord arterial and venous blood. These serve as a baseline to assess the severity of the neonatal hypoxia and acidosis.

A stepwise sequence of procedures is necessary to enable a smooth transition to a normal metabolic state (Figure 8-18).

FIGURE 8-18 A time-based approach to the possible resuscitation of a normal and apneic or cyanotic newborn.

(Used with permission of the American Academy of Pediatrics: Summary of Major Changes to the 2005 AAP/AHA Emergency Cardiovascular Care Guidelines for Neonatal Resuscitation: Translating Evidence-Based Guidelines to the NRP. Vol 15, No. 2, Fall/Winter 2005.)