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 delivery (VBAC). Specifically, after a steady increase in the overall U.S. cesarean delivery rate beginning in the early 1960s, a modest decline in this rate was observed that 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 plummeted to approximately 15%, and the rate of successful TOLAC has also had declined. Given that it has been suggested that about two thirds of women with a prior cesarean delivery are actually 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%, suggest significant underuse of TOLAC in this country. Given this information and the fact that 10% of the obstetric population has had a previous cesarean delivery, more widespread use of TOLAC has the potential to decrease the overall rate of cesarean delivery.

United States total cesarean delivery rate from 1990 through 2008 and the primary cesarean delivery and vaginal birth after cesarean (VBAC) rates from 1990 through 2004.

(Modified from MacDorman M, DeClercq E, Menacker F. Recent trends and patterns in cesarean and vaginal birth after cesarean deliveries in the United States. Clin Perinatol. 2011;38;179-192.)

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 20 years.

In 1999, ACOG issued a practice bulletin acknowledging that while the risks of TOLAC were apparently small in magnitude, clinically significant risks of uterine rupture did exist, with 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 no longer offer 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 of 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 2010 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 a TOLAC.

In response to a growing body of evidence that indicates restriction of a women’s access to TOLAC-VBAC, despite two recent 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 need to 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 the need to reassess this recommendation with reference to other obstetric complications of comparable risk given limited physician and nursing resources.

The ACOG 2010 practice bulletin acknowledged a background of limited access to TOLAC-VBAC evolving over time as well as the recommendation by the NIH panel to facilitate access. Although again recommending that TOLAC-VBAC be undertaken in facilities with staff immediately available to provide emergency care, ACOG recognized 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 was 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:

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  One or two previous low transverse cesarean deliveries

  
  
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  Clinically adequate pelvis

  
  
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  No other uterine scars or previous rupture

  
  
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  Physicians immediately available throughout active labor capable 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:

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

  
  
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  Previous uterine rupture

  
  
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  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 60% to 80% range, although some data suggest this rate may be lower in contemporary practice. A cross-sectional analysis study 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 successful TOLAC is important because maternal morbidity is lowest among women who achieve VBAC and is greatest among women who fail TOLAC and require a repeat operation. The prior indication for cesarean delivery clearly affects the likelihood of 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 included the variables of maternal age, body mass index (BMI), race and ethnicity, prior vaginal delivery, prior VBAC, and a recurrent indication for the cesarean delivery. After development and internal validation of the model, it was found to be accurate and discriminating and subsequently 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 medical units (MFMU) 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.

Graphic nomogram used to predict probability of vaginal birth after cesarean (VBAC). The nomogram is used by locating each patient characteristic and finding the number of points on the uppermost scale to which that characteristic corresponds. The sum of total points predicts the probability of VBAC on the lower scale. BMI, body mass index.

(Modified from Grobman WA, Lai Y, Landon MB, et al, for the National Institute of Child Health and Human Development [NICHD] Maternal Fetal Medicine Units Network [MFMU]. Development of a nomogram for prediction of vaginal birth after cesarean delivery. Obstet Gynecol. 2007;109:806-812.)

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 for 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 those 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%, 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 the 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.

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.

Multiple Prior Cesarean Deliveries

Women with more than one prior cesarean delivery have been demonstrated to have a lower likelihood of achieving VBAC ( Table 20-2 ). Caughey and colleagues reported a 75% success rate for women with one prior cesarean delivery compared with 62% in women with two prior operations. In contrast, a larger multicenter study of 13,617 women undergoing a TOLAC revealed a 75.5% success rate for women with two prior cesarean deliveries, which was not statistically different from the 75% success rate in women with one prior operation.

Uterine Rupture

The principal risk associated with TOLAC is uterine rupture. This complication is directly attributable to TOLAC because symptomatic rupture is rarely observed in planned repeat operations. It is important to differentiate between uterine rupture and uterine scar dehiscence . This distinction is clinically relevant because dehiscence most often represents an occult scar separation observed at laparotomy in women with a prior cesarean delivery. With uterine dehiscence, the serosa of the uterus is intact and hemorrhage, with its potential for fetal and maternal sequelae, is absent. In contrast, uterine rupture is a through-and-through disruption of all uterine layers, with potential consequences of nonreassuring fetal status and perinatal mortality along with severe maternal morbidity, hemorrhage, and mortality. Terminology, definitions, and ascertainment for uterine rupture vary significantly in the existing VBAC literature. A review of four observational studies reported the risks of symptomatic uterine rupture in the TOLAC group and elective repeat cesarean group to be 0.47% (95% confidence interval [CI], 0.28% to 0.77%) and 0.026% (95% CI, 0.009% to 0.082%), respectively. The large multicenter MFMU Net­work Study reported a 0.69% frequency of uterine rupture, with 124 symptomatic ruptures occurring in 17,898 women undergoing TOLAC.

The rate of uterine rupture depends both on the type and location of the previous uterine incision ( Table 20-3 ). Uterine rupture rates are highest with a previous classical or T-shaped incision, with a range reported between 4% and 9%. The risk for rupture with a previous low vertical incision has been difficult to estimate owing to imprecision with the diagnosis and the uncommon use of this incision type. Naif and colleagues reported a 1.1% risk for rupture in 174 women with a prior low vertical scar undergoing TOLAC, whereas Shipp and associates reported a 0.8% (3 of 377) risk for rupture with a prior low vertical incision. On the basis of these two studies, the authors concluded that women with a prior low vertical uterine incision are not at significantly increased risk for rupture compared with women with a prior low transverse incision.

Women with an unknown incision type do not appear to be at increased risk for uterine rupture. Among 3206 women with an unknown scar in the MFMU Network Cesarean Registry, uterine rupture occurred in 0.5% of women undergoing TOLAC. Nevertheless, this frequency is a reflection of the fact that in a contemporary setting, most women with unknown scars will have had a prior low transverse incision. In counseling women with an unknown scar, the physician should attempt to understand whether a prior cesarean delivery had been performed under circumstances in which it was more likely that a different type of incision had been used. For example, a history of preterm cesarean delivery should warrant caution, especially in the setting of malpresentation, because the incision may have involved an undeveloped muscular portion of the uterus, or it may have been a classical incision. For these reasons, if the clinician suspects that the prior delivery occurred under circumstances in which an incision that extended into the muscular portion of the uterus was used, we generally proceed with repeat cesarean delivery.

The most serious sequelae of uterine rupture include perinatal death, hypoxic-ischemic encephalopathy (HIE), and hysterectomy. Citing six perinatal deaths in 74 uterine ruptures among 11 studies, Guise and colleagues calculated 0.14 additional perinatal deaths per 1000 TOLACs. This figure is remarkably similar to that from the NICHD MFMU Network study by Landon and colleagues, in which there were two neonatal deaths among 124 ruptures, for an overall rate of rupture-related perinatal death of 0.11 per 1000 TOLACs. An all-inclusive review of 880 maternal uterine ruptures in studies of varying quality during a 20-year period showed a rate of 0.4 per 1000 ( Table 20-4 ).

Perinatal hypoxic brain injury is another recognized adverse outcome related to uterine rupture. However, estimates of the frequency of perinatal “asphyxia” have varied in the literature because it has been inconsistently defined in TOLAC studies, and variables such as cord blood gas levels and Apgar scores are reported in only a fraction of cases. Landon and colleagues found a significant increase in the rate of HIE related to uterine rupture among the offspring of women who underwent a TOLAC at term compared with the children of women who underwent a planned repeat cesarean delivery (0.46 per 1000 vs. 0 cases, respectively). In this study of 114 cases of uterine rupture at term, seven infants (6.1%) sustained HIE, and two of these infants died in the neonatal period ( Table 20-5 ).

Maternal hysterectomy also may be a complication of uterine rupture if the defect cannot be repaired or is associated with uncontrollable hemorrhage. In five studies that reported on hysterectomies related to rupture, seven cases occurred in 60 symptomatic ruptures (13%; range, 4% to 27%), indicating that 3.4 per 10,000 women electing a TOLAC sustain a rupture that necessitates hysterectomy. Five of 124 women (4%) included in the NICHD MFMU Network study experienced hysterectomy following rupture. However, hysterectomy also can occur in the setting of a planned repeat cesarean, and some evidence suggests that it is no more likely during a TOLAC than during a planned repeat cesarean delivery. Guise and colleagues, for example, reported that the risk for hysterectomy in women attempting TOLAC was not significantly different than that in those undergoing planned repeat cesareans.

Risk Factors for Uterine Rupture

Rates of uterine rupture vary significantly depending on a variety of associated risk factors. In addition to the type of uterine scar, characteristics of the obstetric history that include the number of prior cesarean and vaginal deliveries, the interdelivery interval, and the uterine closure technique have been reported to be associated with the risk for uterine rupture. Similarly, factors related to labor management, including induction and the use of oxytocin augmentation, have been studied.

Number of Prior Cesarean Deliveries

In a large single-center study of more than 1000 women with multiple prior cesarean deliveries undergoing TOLAC, Miller and colleagues reported uterine rupture in 1.7% of women with two or more previous cesarean deliveries compared with 0.6% in those with one prior cesarean (odds ratio [OR], 3.06; 95% CI, 1.95 to 4.79). Interestingly, the risk for uterine rupture was not increased further for women with three prior cesarean deliveries. Caughey and colleagues conducted a smaller study of 134 women with two prior cesarean deliveries and controlled for labor characteristics as well as obstetric history. These authors reported a rate of uterine rupture of 3.7% among these 134 women, compared with 0.8% in the 3757 women with one previous scar (OR, 4.5; 95% CI, 1.18 to 11.5). Macones and colleagues reported a rate of uterine rupture of 1.8% (20 of 1082) in women with two prior cesarean deliveries compared with 0.9% (113 of 12,535) in women with one prior operation (adjusted OR, 2.3; 95% CI, 1.37 to 3.85). A meta-analysis also suggested a nearly threefold increased risk for uterine rupture with two previous cesarean deliveries (1.59% vs. 0.72%). In contrast, the analysis of Landon and colleagues from the MFMU Network Cesarean Registry found no significant difference in rupture rates in women with one prior cesarean (115 of 16,916 [0.7%]) versus multiple prior cesareans (9 of 975 [0.9%]). It thus appears that even if having had more than one prior cesarean section is associated with an increased risk for uterine rupture, the magnitude of any additional risk is fairly small ( Table 20-6 ). ACOG considers it reasonable to offer TOLAC to women with more than one prior cesarean delivery and to counsel such women based on the combination of other factors that affect their probability of achieving a successful VBAC.

TABLE 20-6

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