Vaginal Birth After Cesarean Delivery

Trends

In a review of contemporary cesarean delivery practice, Zhang and colleagues concluded that one of the most important contributors to the rising cesarean delivery rate in the United States was the decline in vaginal birth after cesarean (VBAC) delivery. Specifically, after a steady increase in the overall US cesarean delivery rate beginning in the early 1960s, a modest decline in this rate was observed; it reached a nadir of 21% in 1996, largely because of an increased rate of allowing a trial of labor after cesarean delivery (TOLAC) that was estimated to exceed 50% ( Fig. 20.1 ). However, by 2006, the TOLAC rate had reached a nadir of approximately 15%, and the rate of successful TOLAC deliveries had also declined. Since 2006, the TOLAC rate has climbed only modestly, with approximately 20% of women with one previous cesarean attempting vaginal childbirth by 2013. Given that the majority of women with a prior cesarean delivery are candidates for a TOLAC, most planned repeat operations are influenced by physician discretion and patient choice. A comparison of TOLAC rates between the United States and several European nations, where TOLAC rates vary between 50% and 70%, suggests significant underuse of TOLAC in the United States. Given this information, more widespread use of TOLAC has the potential to decrease the overall rate of cesarean delivery. Metz and colleagues estimated that if all women who were good candidates for TOLAC attempted vaginal birth, the cesarean rate for this population could be reduced from 70.4% to 25.5%.

The evolution in management of the woman with a prior cesarean delivery can be traced through several American College of Obstetricians and Gynecologists (ACOG) documents and key studies over the past 25 years. In 1988, ACOG published “Guidelines for Vaginal Delivery after a Previous Cesarean Birth,” recommending TOLAC and VBAC as it became clear that this procedure was safe and did not appear to be associated with excess perinatal morbidity compared with repeat cesarean delivery. They recommended that each hospital develop its own protocol for the management of VBAC patients and that in the absence of a contraindication such as a prior classical incision, women who had undergone one prior low transverse cesarean section should be counseled and encouraged to attempt labor. This recommendation was supported by several large case series that attested to the safety and effectiveness of TOLAC. With this information, TOLAC rates exceeded 50% in many institutions. Some third-party payers and managed care organizations began to mandate a TOLAC for women with a prior cesarean delivery. Feeling institutional pressure to lower cesarean rates, physicians began to offer a TOLAC liberally and likely included less than optimal candidates. With the rise in VBAC experience, a number of reports appeared in the literature suggesting a possible increase in uterine rupture and its maternal and fetal consequences. Descriptions of uterine rupture with hysterectomy and adverse perinatal outcomes, including fetal death and neonatal brain injury, set the stage for the precipitous decline in VBAC rates during the past 25 years.

In 1999, ACOG issued a practice bulletin acknowledging that although the risks of TOLAC were apparently small, clinically significant risks of uterine rupture did exist, with the potential for poor outcomes for both women and their infants. It was also recognized that such adverse events during a TOLAC could lead to malpractice suits. ACOG thus recommended that TOLAC be conducted in settings in which a physician capable of performing a cesarean delivery was “immediately available” and that institutions be equipped to respond to emergencies such as uterine rupture. The language in the 1999 document also suggested that instead of “encouraging” TOLAC, women with prior low transverse cesarean deliveries should be “offered” TOLAC. A more conservative approach to TOLAC then followed, with recognition of the need to reevaluate VBAC recommendations.

In the aftermath of the 1999 document, many hospitals began to stop offering planned TOLAC. The role of nonclinical factors in the declined utilization of TOLAC has been reviewed by Korst and colleagues. These authors noted five factors that seem to have influenced VBAC rates: (1) recommendations from opinion leaders and professional guidelines, (2) hospital facilities and cesarean delivery availability, (3) reimbursement, (4) medical liability, and (5) patient-level factors. Among patient-level factors is the consideration that patients are becoming more risk-averse and are thus more comfortable with choosing planned repeat cesarean delivery. The question remains as to whether women are less convinced on their own that VBAC is a reasonable option or whether they are being dissuaded by the health care system. Nonetheless, the 2017 ACOG practice bulletin—consistent with prior publications—concludes that most women with one previous cesarean delivery via a low transverse incision are candidates for TOLAC and should be counseled about and offered this option.

In response to a growing body of evidence indicating restriction of a woman's access to TOLAC-VBAC despite two large-scale contemporary multicenter studies that attest to their relative safety, the National Institutes of Health (NIH) held a consensus development conference concerning VBAC in 2010. The panel at that conference concluded that TOLAC is a reasonable birth option for many women with a previous cesarean delivery. The panel also found that existing practice guidelines and the medical liability climate were restricting access to TOLAC-VBAC and that these factors should be addressed. A specific concern raised was the low level of evidence for the requirement for “immediately available” surgical and anesthesia personnel in existing guidelines and—given limited physician and nursing resources—the need to reassess this recommendation with reference to other obstetric complications of comparable risk. Indeed, the 2017 ACOG Practice Bulletin no longer contains language referencing immediate availability of surgical and anesthesia personnel but instead recommends that TOLAC be attempted in facilities that can provide cesarean delivery for situations that are immediate threats to the life of the woman or fetus.

ACOG recognizes that resources for immediate cesarean delivery may not be available in smaller institutions. In such cases, the decision to offer and pursue TOLAC should be carefully considered by patients and their health care providers. It is recommended that the best alternative may be to refer patients to a facility with available resources.

Candidates for a Trial of Labor After Cesarean

The optimal candidates for planned TOLAC are those women in whom the balance of risks (i.e., as low as possible) and chances of success (i.e., as high as possible) are acceptable to the patient and health care provider. Most women who have had a low transverse uterine incision with a prior cesarean delivery and have no contraindications to vaginal birth should be considered candidates for a TOLAC. The following are selection criteria suggested by ACOG for identifying candidates for TOLAC:

• One or two previous low transverse cesarean deliveries

• A clinically adequate pelvis

• No other uterine scars or previous rupture

• Capability of monitoring labor and performing an emergency cesarean delivery

It should be noted that these criteria identify women who are likely to be reasonable candidates and do not exclude women with any other clinical situation from the option of TOLAC. For example, several studies indicate that it may be reasonable to offer a TOLAC to women with macrosomia, gestation beyond 40 weeks, previous low vertical incision, unknown uterine scar type, and twin gestation.

Conversely, a TOLAC is contraindicated in women at high risk for uterine rupture. A TOLAC should not be attempted in the following circumstances:

• Previous classical or T-shaped incision or extensive transfundal uterine surgery

• Previous uterine rupture

• Medical or obstetric complications that preclude vaginal delivery

Success Rates for a Trial of Labor After Cesarean

The overall success rate for a population of women undergoing TOLAC appears to be in the range of 60% to 80%, although some data suggest that this rate may be lower in contemporary practice. A cross-sectional analysis that utilized National Hospital Discharge Survey information noted that TOLAC success rates had fallen from nearly 70% in 2000 to 40% to 50% by 2009.

Predictors of successful TOLAC are well described. The ability to predict a successful TOLAC is important because maternal morbidity is lowest among women who achieve VBAC and greatest among those who fail TOLAC and require a repeat operation. Evidence suggests that women with at least a 60% to 70% likelihood of achieving VBAC experience the same or less maternal morbidity as women who have an elective repeat operation. The prior indication for cesarean delivery clearly affects the likelihood of a successful TOLAC because women with “recurrent” indications (i.e., labor arrest disorders) are less likely to achieve VBAC. Also, a history of prior vaginal birth is associated with the highest success rates for VBAC ( Table 20.1 ). Several authors have developed models for predicting VBAC ( Fig. 20.2 ). Grobman and colleagues developed a model based on factors that could be assessed at the first prenatal visit. These include the variables of maternal age, body mass index (BMI), race and ethnicity, prior vaginal delivery, prior VBAC, and a recurrent indication for a cesarean delivery. After development and internal validation of the model, it was found to be accurate and discriminating; subsequently it has been validated in populations other than that in which it was developed. The calculator is available online at mfmu.bsc.gwu.edu . Because circumstances at the time of admission for delivery may affect the chance of successful TOLAC, a second calculator was created to take these factors into account and is also available at the maternal-fetal medicine units (MFMUs) site. The additional factors include maternal BMI at delivery, cervical status, need for induction, and the presence or absence of preeclampsia. A simple admission model and scoring system for the prediction of VBAC success that incorporates cervical status, history of vaginal birth, maternal age, prior indication for cesarean delivery, and maternal BMI has also been investigated by Metz and colleagues.

A summary of factors associated with VBAC in the setting of TOLAC is summarized in the following sections.

Maternal Demographics

Race, age, BMI, and insurance status have all been demonstrated to be associated with the success of TOLAC. In a multicenter study of 14,529 term pregnancies in which TOLAC was attempted, white women had a 78% success rate, compared with 70% in nonwhite women. Obese women are more likely to fail a TOLAC, as are women older than 40 years. Conflicting data exist with regard to payer status.

Prior Indication for Cesarean Delivery

Success rates for women whose first cesarean delivery was performed for a nonrecurring indication (breech, nonreassuring fetal well-being) are similar to vaginal delivery rates for nulliparous women. Prior cesarean delivery for a breech presentation is associated with a reported success rate of 89%. In contrast, prior cesarean delivery for cephalopelvic disproportion (CPD) or failure to progress (FTP) has been associated with success rates that range from 50% to 67%.

Prior Vaginal Delivery

Prior vaginal delivery, including prior VBAC, is one of the greatest predictors of successful TOLAC. In one series, women with a prior vaginal delivery had an 87% TOLAC success rate, compared with a 61% success rate in women without a prior vaginal delivery. Caughey and colleagues reported that for patients with a prior VBAC, the success rate was 93%, compared with 85% in women with a vaginal delivery before their cesarean birth but who had not had a successful VBAC. Mercer and colleagues noted that the success rate increased from 87.6% with one prior vaginal delivery to 90.0% in women with two prior successful attempts.

Birthweight

Increased birthweight is associated with a lower likelihood of a successful VBAC. Birthweight greater than 4000 g, in particular, is associated with a higher risk for failed VBAC. Although some report success rates below 50%, particularly in women with no prior vaginal delivery, others have documented that as many as 60% to 70% of women who attempt VBAC with a macrosomic fetus are successful. Peaceman and colleagues reported a 34% success rate when the second pregnancy birthweight exceeded the first by 500 g and the prior indication was dystocia, compared with a 64% success rate with other prior indications. It should be noted that although birthweight has been associated with the success of VBAC, this factor cannot be known with precision prior to undertaking TOLAC, and it has not been demonstrated to what degree estimated fetal weight is associated with VBAC.

Labor Status and Cervical Examinations

Both labor status and cervical examination on admission influence the success of a TOLAC. Flamm and Geiger reported an 86% success rate in women who presented in labor with cervical dilation greater than 4 cm. Conversely, the VBAC success rate dropped to 67% if the cervix was dilated less than 4 cm on admission.

Not surprisingly, women who undergo induction of labor are at higher risk for repeat cesarean delivery compared with those who enter spontaneous labor. Data from the National Institute of Child Health and Human Development (NICHD) MFMU Cesarean Registry demonstrated a 67.4% success rate in women who underwent induction versus 80.5% in those who underwent spontaneous labor. In a study of 429 women undergoing induction with a prior cesarean delivery, Grinstead and Grobman reported an overall 78% success rate. These authors noted several factors related to labor induction as determinants of VBAC success, including indication for induction and the need for cervical ripening. Grobman and colleagues have also reported a VBAC success rate of 83% in 1208 women with a prior cesarean delivery and prior vaginal delivery undergoing induction of labor.

Although induction is associated with lower rates of VBAC than spontaneous labor, data from retrospective observational cohort studies have shown that as compared with expectant management, labor induction in women undergoing TOLAC is associated with lower odds of cesarean delivery at 39 weeks’ gestation and beyond.

Previous or Unknown Incision Type

Previous incision type cannot be ascertained in certain patients. Nevertheless, it appears that women whose previous incision type is unknown have VBAC success rates similar to those of women with documented prior low transverse incisions. Similarly, women with previous low vertical incisions do not appear to have lower VBAC success rates.