Williams Manual of Pregnancy Complications, 23 ed.

CHAPTER 18. Prior Cesarean Delivery

Few conditions in modern obstetrics have been as controversial as the management of a woman with a prior cesarean delivery. For decades, the scarred uterus was believed to contraindicate labor out of fear of uterine rupture. With the escalation of cesarean delivery rates, interest in vaginal birth after cesarean (VBAC) developed in an attempt to reduce the rapid rise. In 1978, only 2 percent of American women who had previously undergone cesarean birth were attempting vaginal delivery. With the support and encouragement of American College of Obstetricians and Gynecologists (ACOG) and a 1980 National Institute of Health (NIH) consensus conference on VBAC supporting an increased utilization of VBAC, the rate increased to 28.3 percent by 1996.

As the frequency of VBAC increased throughout the 1990s, a number of reports confirmed an increased maternal and perinatal morbidity associated with trial of labor. Uterine rupture occurs 1 in 120 trials of labor with the risk of death or neurologic injury to the fetus occurring in approximately 10 percent of those suffering a uterine rupture.

In response ACOG issued guidelines in 1999 stating that women should attempt trial of labor only in appropriately equipped institutions with physicians who are “readily available” to provide emergency care should a uterine rupture occur. As a result of the ACOG guidelines in combination with medicolegal concerns on behalf of physicians and hospitals, the VBAC rate has fallen to an all time low of 8 percent in 2007.

The NIH in 2010 convened a consensus conference on VBAC and issued a report regarding risks and benefits of trial of labor. Similarly in 2010, ACOG issued a practice bulletin regarding management of vaginal birth after cesarean.

CHOOSING THE ROUTE OF DELIVERY

When counseling a woman with a prior cesarean delivery there are multiple factors known to affect the likelihood of successful vaginal delivery and are shown in Table 18-1. Counseling should begin early in pregnancy with frequent reassessments of various risk factors throughout pregnancy (Table 18-2). The highest successful VBAC rates occur in women with, a prior vaginal delivery, the woman presenting in active labor with advanced cervical dilation, and in those women whose prior indication for cesarean delivery was fetal malpresentation. Women who have never undergone a prior vaginal delivery, those who require induction of labor, postterm pregnancies and those admitted with an unfavorable cervix are less likely to be successful in their pursuit of VBAC. Unfortunately, there are no screening tools that have been clinically useful in predicting adverse outcomes associated with a trial of labor.

TABLE 18-1. Factors Affecting the Likelihood of Successful Trial of Labor

image

TABLE 18-2. Counseling of the Woman with a Prior Cesarean Delivery

image

FACTORS TO CONSIDER IN CANDIDATES FOR A TRIAL OF LABOR

Type of Prior Uterine Incision

Women with a single prior low transverse uterine scar and undergo a trial of labor have a 60 to 70 percent chance of a successful vaginal birth and have the lowest risk of uterine rupture. The risk of uterine rupture in women with one prior low transverse uterine incision is 0.7 percent compared with 2.0 percent in women with a prior low vertical uterine scar and 1.9 percent with a prior classical or either T or J incision (Table 18-3).

TABLE 18-3. Risk of Uterine Rupture Based on Type of Uterine Incision

image

A prior vaginal delivery in a woman with a previous low transverse uterine incision significantly reduces the likelihood of uterine rupture. Conversely, women with a prior uterine rupture experience a recurrence of uterine rupture in 6 to 32 percent depending on the site of the prior rupture and should therefore be counseled to undergo a repeat cesarean delivery prior to the onset of labor once lung maturity is confirmed.

Multiple Prior Cesarean Deliveries

The risk of uterine rupture increases with the number of previous uterine incisions and is variably reported between 0.9 percent and 3.7 percent. Any previous vaginal delivery, either before or after the prior cesarean birth, significantly improves the likelihood for a successful VBAC.

Indication for Prior Cesarean

Overall, the success rate for a trial of labor is significantly related to the indication for the prior cesarean. Women with a prior cesarean delivery for fetal malpresentation have a 75-percent likelihood of successful TOL compared with 60-percent when performed for nonreassuring fetal heart patterns and the success rate falls to 54-percent if the original indication was failure to progress or cephalopelvic disproportion.

Multifetal Gestation

Although, most studies report that women with multifetal gestation are less likely to pursue a trial of labor after cesarean (TOLAC), the likelihood of a successful VBAC was similar to singleton gestations and the overall risk for uterine rupture was not found to be increased. However, a failed trial of labor was observed to significantly increase the risk of uterine rupture in 1.4 percent compared with 0.2 percent in those women with a successful VBAC.

LABOR AND DELIVERY CONSIDERATIONS

Informed Consent

No woman should be mandated to undergo a trial of labor. The risks and benefits of a trial of labor versus a repeat cesarean delivery should be discussed with any woman with a prior uterine incision. The following issues should be addressed:

1. Advantages of successful vaginal delivery, that is, shorter hospital stay, less postpartum discomfort, more rapid recovery, and the like

2. Risks of trial of labor—to include the risk of uterine rupture (approximately 1 percent) and, in the event of uterine rupture, a 10 percent risk of neonatal death or neurologic injury

3. Factors that increase the risk of failed trial of labor and uterine rupture

4. Contraindications to a trial of labor, for example, prior classical cesarean, placenta previa, and others

5. Despite the best available care and resources, catastrophic uterine rupture leading to perinatal death or injury occurs 1 per 1000 trials of labor

Cervical Ripening and Labor Stimulation

Multiple reports confirm both an increased risk of failed trial of labor and uterine rupture when labor stimulation is required. The 2010 ACOG VBAC practice bulletin on the basis of limited or inconsistent scientific evidence (Level B) recommends that induction of labor for maternal or fetal indications remain an option but cautions that women should be informed of the potential increased risk of uterine rupture and the potential decreased possibility of achieving VBAC. Further the ACOG bulletin indicates that Misoprostol should not be used for the third-trimester cervical ripening or induction of labor in patient with a prior cesarean delivery or major uterine surgery.

Epidural Analgesia

Although the use of epidural analgesia has been debated in the past out of fear that such a technique might mask the pain of uterine rupture, there is no evidence to support withholding epidural analgesia in women attempting VBAC. Because the risks associated with a trial of labor and uterine rupture may be catastrophic and unpredictable, a joint statement in 2008 by ACOG and the American Society of Anesthesiologist (ASA) recommends that trial of labor should be undertaken in facilities with immediate availability of appropriate facilities and personnel, including obstetric anesthesia and a physician capable of monitoring labor and performing an emergency cesarean delivery.

UTERINE RUPTURE

The most feared complication associated with a trial of labor is that of uterine rupture. It is important to differentiate between uterine rupture and uterine scar dehiscence. Uterine rupture refers to complete disruption of all uterine layers to include serosa and is associated with maternal hemorrhage, extrusion of fetus or placenta and adverse fetal outcomes. Uterine dehiscence refers to an incomplete, clinically occult, uterine scar separation with the serosa remaining intact. Uterine dehiscence is often referred to as a “window.” Factors reported to be associated with an increased risk of uterine rupture include lower Bishop score on admission to labor and delivery, increasing maternal age, advancing gestational age, birth weight exceeding 4000 g, and short interdelivery intervals. There are no clinically useful screening tools that reliably predict uterine rupture.

Uterine rupture most commonly presents with fetal heart rate decelerations (Figure 18-1). Other symptoms such as abdominal pain, vaginal bleeding, and uterine contraction abnormalities occur less frequently.

image

FIGURE 18-1 Internal monitor tracing demonstrates fetal heart rate decelerations, increase in uterine tone, and continuation of uterine contractions in a woman with uterine rupture. (From Rodriguez MH, Masaki DI, Phelan JP, Diaz FG: Uterine rupture: Are intrauterine pressure catheters useful in the diagnosis? Am J Obstet Gynecol 161:666, 1989, with permission.)

Management of uterine rupture includes emergency cesarean delivery, treatment of maternal hemorrhage, and either repair of the uterine defect or hysterectomy. Neonatal outcome associated with uterine rupture results in neonatal death or hypoxic ischemic encephalopathy in 10 percent. Even prompt intervention did not prevent all cases of severe neonatal acidosis, neonatal morbidity and mortality attributed to uterine rupture.

ELECTIVE REPEAT CESAREAN DELIVERY

Compared with vaginal delivery, cesarean birth is associated with increased risks, including anesthesia, hemorrhage, damage to the bladder and other organs, pelvic infection, and adhesions. In spite of these risks, an elective repeat cesarean is considered by many women to be preferable to attempting a trial of labor. Frequent reasons for this preference include convenience of a scheduled delivery, sterilization at the time of delivery, and fear of failed trial of labor.

If the woman desires an elective scheduled repeat cesarean delivery, it is essential that the fetus be mature and unless dictated by medical or obstetric conditions, delivery should be considered no earlier than 39 weeks’ gestation (see Table 18-4). Alternatively, awaiting the onset of spontaneous labor is certainly acceptable.

TABLE 18-4. Fetal Lung Maturity

image


For further reading in Williams Obstetrics, 23rd ed.,

see Chapter 26, “Prior Cesarean Delivery.”