Some obstetricians allow a trial of labor after a previous low-vertical uterine incision provided that there is documentation that the uterine incision was confined to the lower uterine segment (low-vertical uterine incisions often extend above the lower uterine segment, especially when performed in preterm patients). Martin et al. reviewed the obstetric literature to summarize outcomes among women who attempted VBAC after a previous low-vertical cesarean delivery. The authors were able to identify 10 studies reporting the complete outcomes for 372 patients. Although four (1%) uterine ruptures were described, only two ruptures involved the previous low-vertical incision; the other two ruptures occurred at uterine sites anatomically remote from the previous scar. Therefore, the authors concluded that a low-vertical incision that does not extend beyond the lower uterine segment should not be a contraindication to TOLAC in uncomplicated singleton pregnancies. The ACOG concluded that there is no consistent evidence of an increased risk for uterine rupture in women with a previous low-vertical uterine incision and that obstetricians and patients may choose to undergo TOLAC in the presence of a documented prior low-vertical uterine incision.

For some patients, there is no documentation of the type of uterine incision performed during a previous cesarean delivery. Some obstetricians require documentation of the type of previous uterine incision before they allow a patient to attempt VBAC. Smith et al. found that the incidence of uterine rupture did not differ in women with an unknown scar compared to those with a known low-transverse uterine incision. An explanation for this finding is that most patients with an unknown uterine scar have a low-transverse uterine incision scar from the previous cesarean delivery. Ultrasonography may help the obstetrician confirm the presence of a low-transverse uterine scar in the pregnant woman with an unknown uterine scar. The ACOG concluded that “women with one previous cesarean delivery with an unknown uterine scar type may be candidates for TOLAC, unless there is a high clinical suspicion of a previous classical uterine incision, such as cesarean delivery performed at an extremely preterm gestational age.”

Results of studies that have assessed outcomes of TOLAC in women with a history of more than one cesarean delivery are inconsistent. One large multicenter study found no increased risk for uterine rupture (0.9% versus 0.7%) in women with more than one previous cesarean delivery compared to women with only one previous cesarean delivery. A second large study observed that the risk for uterine rupture increased from 0.9% to 1.8% during TOLAC in women with two previous cesarean deliveries. Both studies observed that TOLAC was associated with an increase in maternal morbidity in women with more than one previous cesarean delivery, although the absolute magnitude of the difference in morbidity was relatively small. Data regarding the risk for TOLAC in women with more than two previous cesarean deliveries are limited. The ACOG concluded that it is reasonable to consider TOLAC for women with two previous low-transverse cesarean deliveries. The Royal College of Obstetricians and Gynaecologists (RCOG) stated that “women who have had two or more prior lower segment caesarean deliveries may be offered VBAC after counseling by a senior obstetrician,” while the Society of Obstetricians and Gynaecologists of Canada (SOGC) advises that “women with 2 prior Caesarean sections appear to have similar vaginal birth after Caesarean rates as those with 1 prior Caesarean section. Women should be informed of a higher risk of uterine rupture in trial of labor after Caesarean with more than 1 Caesarean section.” The VBAC prediction model developed for singleton gestation was found to be valid for predicting VBAC success in women with two prior cesarean deliveries.

Some obstetricians believe that uterine overdistention, which occurs with twin gestation, increases the risk for uterine rupture in patients with a history of previous cesarean delivery. Studies consistently suggest otherwise but are limited by the small number of patients. Cahill et al. performed a retrospective cohort study of 25,005 obstetric patients with at least one previous cesarean delivery, which included 535 patients with a twin pregnancy. The investigators observed that women with a twin gestation were less likely to attempt VBAC, but were no more likely to have a failed VBAC or to experience major morbidity than women with a singleton gestation. Likewise, a report from the Maternal-Fetal Medicine Unit Cesarean Registry included outcome measures for 186 women with a twin gestation who attempted VBAC; 120 (64.5%) delivered vaginally. Women who attempted TOLAC with twin gestation had no higher risk for transfusion, endometritis, intensive care unit admission, or uterine rupture than women who underwent elective repeat cesarean delivery. The investigators concluded that TOLAC in women with a twin gestation after previous cesarean delivery does not appear to be associated with a higher risk for maternal morbidity.

In contrast, another large population study by Ford et al. reported a statistically significant increase in uterine rupture rate associated with TOLAC compared with elective cesarean delivery for twin gestation. The authors reviewed outcomes of 6555 women with a twin gestation who delivered between 1993 and 2002. Among 1850 women who underwent TOLAC, 836 (45.2%) delivered vaginally. The rate of uterine rupture was higher in the TOLAC group compared to the elective cesarean delivery group (0.9% versus 0.1%), but the rate of wound complications was lower in the TOLAC group (0.6% versus 1.3%).

The ACOG concluded that “women with one previous cesarean delivery with a low-transverse [uterine] incision, who are otherwise appropriate candidates for twin vaginal delivery, are considered candidates for TOLAC.” While the SOGC guidelines are aligned with the ACOG, the RCOG takes a more conservative approach, stating that “there is uncertainty about the safety and efficacy of planned VBAC in pregnancies complicated by … twin gestation.”

The ACOG’s stance on macrosomia (fetal weight > 4000 g) and TOLAC eligibility has shifted over the years. In 1994 the ACOG concluded that macrosomia does not contraindicate TOLAC. However, in 1999, the ACOG revised its recommendations to include suspected macrosomia on the list of TOLAC eligibility criteria that are controversial. While macrosomia is well established as a risk factor associated with reduced success rates of TOLAC, studies examining the incidence of uterine rupture report conflicting results. The 2019 ACOG guidelines encourage providers to consider current fetal weight relative to past birth weights, but concluded that “suspected macrosomia alone should not preclude the possibility of TOLAC.”

Studies have consistently demonstrated decreased rates of successful VBAC in women who undergo TOLAC after 40 weeks’ gestation. The largest study assessing the incidence of uterine rupture in women with advanced gestation undergoing TOLAC did not report an elevated risk in this population. The ACOG acknowledges that the likelihood of successful VBAC may be diminished in more advanced gestations, but a “gestational age greater than 40 weeks alone should not preclude TOLAC.”

Breech presentation itself does not increase the risk for uterine rupture. In contemporary practice, most obstetricians do not allow a trial of labor in any patient with a breech presentation. Thus, most patients with a breech presentation undergo elective cesarean delivery, with or without a history of previous cesarean delivery. The ACOG concluded that external cephalic version is not contraindicated in women with breech presentation and a previous low-transverse uterine incision who are at low risk for adverse maternal and neonatal outcomes from external cephalic version and TOLAC.

Some women reject TOLAC because they have experienced prolonged, painful labor during a previous pregnancy. They fear that they will again experience a prolonged, painful labor and ultimately need a repeat cesarean delivery. This fear is more common in women who have delivered in smaller hospitals without the availability of neuraxial analgesia during labor. Other women reject TOLAC because they prefer to schedule the date of elective repeat cesarean delivery, permitting prearrangement of responsibilities such as childcare. Kirk et al. questioned 160 women regarding factors affecting their choice between TOLAC and elective repeat cesarean delivery. These investigators concluded that “social exigencies appeared to play a more important role than an assessment of the medical risks in making these decisions.” Similarly, Joseph et al. observed that fear and inconvenience are the most common deterrents to attempted VBAC. Finally, some women reject TOLAC because of their concern about the adverse effects of labor and vaginal delivery on the maternal pelvic floor, with the risk for subsequent problems such as urinary and fecal incontinence.

A lack of appropriate education and counseling may also contribute to low TOLAC rates. Several survey studies have reported that TOLAC-eligible women are not adequately informed about the risks and benefits of TOLAC compared with elective repeat cesarean delivery. Bernstein et al. found that only 4% of eligible patients electing a repeat cesarean delivery knew that the success rate of TOLAC could be as high as 60% to 80%, and more than half were unaware that the recovery from a cesarean is longer than with vaginal delivery. Alarmingly, one study found that 62% of TOLAC-eligible women had received counseling recommending a repeat elective cesarean delivery without mention of TOLAC, despite having at least three antenatal visits. The impact of patient education cannot be understated; Sindiani et al. reported that the single independent factor that influenced a woman’s choice of mode of delivery was whether the woman received counseling on the risks of TOLAC. Women counseled on the risks of TOLAC were four times more likely to elect a TOLAC than those not counseled. Interestingly, some studies have reported that women establish their initial preference for mode of delivery based on outside sources of information and opinion from friends and family; subsequent antenatal counseling by a medical professional had limited effect or influence on their final decision. However, provider bias during counseling can have a significant impact, as patients are much more likely to select a mode of delivery if they perceive it to be a strong provider preference.

Cox discussed and emphasized the importance of shared decision-making when choosing the mode of delivery after a previous cesarean. Patient-centered decision aids have been suggested as tools to assist providers and patients in this process, and perhaps improve education in effort to increase the TOLAC rate. However, the PROCEED trial, a multicenter study of 1485 patients, failed to show that use of a decision support tool influenced the TOLAC rate compared with usual care (43.3% versus 46.2%). Regardless of how one approaches a shared decision-making conversation, it is important to include a discussion about a patient’s family planning goals, as the risk for a placenta accreta spectrum and major hemorrhage in subsequent pregnancies increases with each cesarean delivery (see Chapter 37 ). A patient who is planning to have several children should take this into consideration when deciding between TOLAC and repeat cesarean delivery. In 2019, the ACOG emphasized: “After counseling, the ultimate decision to undergo TOLAC or a repeat cesarean delivery should be made by the patient in consultation with her obstetrician or obstetric care provider. The potential risks and benefits of both TOLAC and elective repeat cesarean delivery should be discussed. Documentation of counseling and the management plan should be included in the medical record.”

In addition to patient preferences, the low frequency of TOLAC has resulted, in part, from physician preferences. One survey of privately practicing obstetricians revealed the most common reasons for discontinuing TOLAC in their clinical practice included maternal-fetal safety concerns about uterine rupture and medicolegal consequences. Physicians who did not offer TOLAC to their patients were more likely to have been in practice less than 10 years, report previous experience with a morbid uterine rupture, and indicate prior involvement in medical malpractice litigation.

In many cases, physician reimbursement is greater for elective repeat cesarean delivery than for VBAC, despite the fact that VBAC requires greater physician effort. Stafford reviewed the impact of nonclinical factors on the performance of repeat cesarean delivery in California. He observed that “proprietary hospitals, with the greatest incentive to maximize reimbursement, had the highest repeat cesarean [delivery] rates.” Nonteaching hospitals and hospitals with low-volume obstetric services had lower VBAC rates than teaching hospitals and hospitals with high-volume obstetric services. Likewise, Hueston and Rudy found that women who undergo elective repeat cesarean delivery are more likely to have private insurance than women who attempt VBAC. Stafford concluded: “Because a cesarean [delivery] is nearly twice as costly as a vaginal birth, … the higher repeat cesarean [delivery] rates associated with proprietary hospitals, non-teaching hospitals, and low-volume hospitals contribute to increased health care expenditures.” Furthermore, a 2017 systematic review by Rogers et al. determined, “After a review of all the available evidence, we conclude that for women who are likely to have a successful vaginal delivery, routine elective repeat cesarean delivery may result in excess morbidity and cost from a population perspective.”

From an individual patient perspective, evaluating the cost effectiveness between the two modes of delivery is complex and involves several factors, the most important of which is the likelihood of a successful VBAC. A failed TOLAC requiring a subsequent cesarean delivery may offset any financial benefit initially anticipated, particularly if the delivery becomes an emergency or results in serious maternal or neonatal morbidity. One analytic model examining marginal cost per quality-adjusted life years determined TOLAC to be more cost-effective than an elective repeat cesarean when the predicted VBAC success rate is greater than 47.2%.

Uterine rupture is one of the most morbid complications of TOLAC. Unfortunately, there is inconsistency and confusion in reports of the incidence of asymptomatic uterine scar dehiscence as opposed to frank uterine rupture. Uterine scar dehiscence may be defined as a uterine wall defect that does not result in fetal compromise or maternal hemorrhage and that does not require emergency cesarean delivery or postpartum laparotomy. In contrast, uterine rupture may be accompanied by extrusion of the fetus or placenta and results in fetal compromise, maternal hemorrhage, or both, sufficient to require cesarean delivery or postpartum laparotomy.

Obstetricians understandably fear that they will be found liable if an adverse event occurs during TOLAC. In one case, a jury awarded a verdict of $98.5 million because of a delayed diagnosis of uterine rupture. Phelan cited another court decision that he predicted would have a “chilling effect on the future of VBAC.” In this case, the fetal heart rate (FHR) was normal until it abruptly decreased to 80 beats per minute at a cervical dilation of 9 cm. The interval between the onset of the FHR deceleration and emergency cesarean delivery was 27 minutes. At delivery, the fetal head was found in the left adnexa. The mother required transfusion, and the child suffered from developmental delay and cerebral palsy. The court found that the defendants were negligent in their failure to deliver the infant in a timely manner and to provide adequate informed consent. The court also concluded that “the ACOG 30-minute rule represented the maximum period of elapse” and did not represent the minimum standard of care. As a result of this verdict, Phelan proposed the use of a VBAC consent form that includes the following statement: “I understand that if my uterus ruptures during my VBAC, there may not be sufficient time to operate and to prevent the death of or permanent brain injury to my baby.” Flamm responded that “widespread implementation of this or similar consent forms essentially would mean the end of VBAC.”

Greene wrote a sobering editorial on the risks associated with attempted VBAC. Observing that the study performed by Lydon-Rochelle et al. found that spontaneous labor following a cesarean delivery was associated with a tripling of the risk for uterine rupture (i.e., a uterine rupture rate of 5.2 per 1000 women who had spontaneous onset of labor versus 1.6 per 1000 women who underwent elective repeat cesarean delivery without labor), he stated that “there is no reason to believe that improvements in clinical care can substantially reduce the risks of uterine rupture and perinatal mortality.” Greene concluded his 2001 editorial as follows:

After a thorough discussion of the risks and benefits of attempting a vaginal delivery after cesarean section, a patient might ask, “But doctor, what is the safest thing for my baby?” Given the findings of Lydon-Rochelle et al., my unequivocal answer: elective repeat cesarean section.

An analysis of obstetric closed claims cases determined that 80% of claims involving TOLAC could be avoided if TOLAC was offered only to women who present in spontaneous labor, follow a normal labor curve without augmentation, and maintain a favorable FHR tracing. While adoption of this strategy may reduce litigation, its conservative nature would greatly restrict the number of candidates eligible for TOLAC.

Most studies of VBAC have been conducted in university or tertiary care hospitals with in-house obstetricians, anesthesia providers, and operating room staff. However, a 2007 study evaluated outcomes for women who attempted VBAC in 17 diverse hospitals, including six university hospitals, five community hospitals with an obstetrics-gynecology residency program, and six community hospitals without an obstetrics-gynecology residency program. The incidence of uterine rupture with attempted VBAC was significantly higher in community hospitals than in university hospitals (1.2% versus 0.6%, respectively), but the rates of maternal blood transfusion and composite adverse maternal outcome were identical in community and university hospitals. However, several studies have demonstrated worse neonatal outcomes when TOLAC is attempted in out-of-hospital birth settings, such as the home or at a birthing center.

The ACOG and the Society for Maternal-Fetal Medicine have recommended that attempted VBAC should occur in a level I center or higher (see Table 11.3 ). Furthermore, the ACOG, RCOG, and SOGC specify that emergency equipment and personnel should be immediately available. Critics have suggested that these guidelines are too restrictive and ultimately limit women’s access to TOLAC, particularly at smaller centers and in more rural areas.

In 1999, the ACOG issued guidelines stating that because uterine rupture may be catastrophic, TOLAC should be attempted in institutions equipped to respond to emergencies with physicians immediately available to provide emergency care. However, the ACOG also noted that “the operational definition of ‘immediately available’ personnel and facilities remains the purview of each local institution.” Likewise, the RCOG has stated that planned VBAC should be conducted in a facility “with resources available for immediate caesarean delivery and advanced neonatal resuscitation.”

The 2010 NIH consensus development panel noted that approximately one-third of hospitals and one-half of obstetric physicians in the United States no longer offered TOLAC, largely because of fear of liability and litigation. The panel expressed concern that practice guidelines have created barriers that prevent women from choosing TOLAC and that pregnant women should be given the opportunity to make informed decisions about the risks and benefits of TOLAC versus elective repeat cesarean delivery. The panel also urged professional societies to reassess the requirement for immediate availability of surgical and anesthesia providers.

Subsequently, the ACOG stated that restricting access was not the intention of their “immediately available” requirement. The ACOG noted that “much of the data concerning the safety of TOLAC is from centers capable of performing a timely emergency cesarean delivery.” Further, they stated that “although there is reason to think that more rapid availability of cesarean delivery may provide a small incremental benefit in safety, comparative data examining in detail the effect of alternate systems and response times are not available.”

Holmgrem et al. reviewed neonatal outcomes of 36 uterine ruptures occurring in 11,195 TOLAC cases from 2000 to 2009. The primary outcome was an Apgar score < 7 or umbilical artery pH < 7.0. The authors emphasized that mere minutes count; the mean (standard deviation) decision-to-delivery times for neonates with and without adverse outcomes were 23.3 (±10.8) and 16.0 (±7.7) minutes, respectively ( P =.02). In 2018, Al-Zirqi et al. reviewed 41 years of population-based registry data to investigate the infant outcomes after uterine rupture. They concluded that decision-to-delivery time of less than 20 minutes limited the incidence of infant death. In comparison, a decision-to-delivery time > 30 minutes increased the odds of infant death over 16-fold. Birnbach et al. reviewed the impact of anesthesia provider availability on the incidence of VBAC in the United States. They concluded that the “immediately available” requirement necessitates having an in-hospital anesthesia provider who is not performing another simultaneous anesthetic. Their economic analysis prompted a conclusion that “the minimum requirement to provide immediate anesthesia care for all deliveries would be to have all deliveries at facilities with greater than 1500 deliveries annually.”

In 2019, the ACOG modified their practice bulletin as follows:

Women attempting TOLAC should be cared for in a level I center or higher. Level I facilities must have the ability to begin emergency cesarean delivery within a time interval that best considers maternal and fetal risks and benefits with the provision of emergency care… The decision to offer and pursue TOLAC in a setting in which the option of emergency cesarean delivery is limited should be carefully considered by patients and their obstetricians or other obstetric care providers .

Further, the ACOG also encourages respect for patient autonomy, as follows:

Respect for patient autonomy also dictates that even if a center does not offer TOLAC, such a policy cannot be used to force women to have cesarean delivery or to deny care to women in labor who decline to have a repeat cesarean delivery .

Similarly, the American Society of Anesthesiologists states, “The immediate availability of appropriate facilities and personnel (including obstetric anesthesia; nursing personnel; and a physician capable of monitoring labor and performing cesarean delivery, including an emergency cesarean delivery) is optimal. When resources for immediate cesarean delivery are not available … patients should be clearly informed of the potential increase in risk and the management alternatives.” Finally, the American Academy of Family Physicians practice guidelines state, “Women at risk of uterine rupture or other complications who are still able to consider [TOLAC/VBAC] need to deliver at facilities that have the ability to effectively manage these complications. Information is lacking about how appropriate [TOLAC/VBAC] may be in different types of facilities … thus, there is little guidance about the settings in which to perform [TOLAC/VBAC] when looking at only the type or location of the facility, or the number of deliveries performed.”

Contraindications to planned TOLAC include :

• •

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

• •

  Previous uterine rupture

• •

  Medical or obstetric complication that precludes labor and vaginal delivery

• •

  Inability to perform emergency cesarean delivery because of unavailable surgeon, anesthesia provider, or operating room staff (see earlier).

In a 2004 systematic review of published studies of attempted VBAC, Guise et al. observed no significant difference in the incidence of maternal death or hysterectomy between women who attempted a trial of labor and those who underwent repeat cesarean delivery. Uterine rupture was more common in the women who attempted a trial of labor, but the rates of asymptomatic uterine dehiscence did not differ.

Wen et al. performed a retrospective cohort comparison of outcomes after TOLAC or elective repeat cesarean delivery in 308,755 Canadian women with a history of previous cesarean delivery. These investigators observed that the rates of uterine rupture (0.65%), transfusion (0.19%), and hysterectomy (0.10%) were significantly higher in the TOLAC group. However, the maternal in-hospital death rate was significantly lower in the TOLAC group (1.6 per 100,000) than in the elective cesarean delivery group (5.6 per 100,000). Similarly, Guise et al. observed a lower maternal mortality rate in women who underwent TOLAC than in women who underwent elective repeat cesarean delivery (0.004% versus 0.013%, respectively).

Rossi and D’Addario performed a metaanalysis of studies published from 2000 to 2007 that compared maternal morbidity in women who underwent TOLAC versus women who underwent elective repeat cesarean delivery. Successful VBAC occurred in 17,905 (73%) of 24,349 women who underwent TOLAC. Overall maternal morbidity did not differ between women who underwent TOLAC and women who underwent elective repeat cesarean delivery. Likewise, the incidence of blood transfusion and hysterectomy did not differ between the two groups. The incidence of uterine rupture was higher in the TOLAC group (1.3% versus 0.4%). Further, maternal morbidity, uterine rupture, blood transfusion, and hysterectomy were more common in women who had a failed TOLAC.

In 2010, the NIH convened a consensus panel to review birth outcomes associated with TOLAC and elective repeat cesarean delivery in developed countries. The panel performed the most comprehensive review of its time, including 41 studies of maternal outcomes and 11 studies of neonatal outcomes. The panel determined the overall benefits of TOLAC “are directly related to having a [successful] VBAC as these women typically have the lowest morbidity.” Likewise, the panel noted that the harms of TOLAC “are associated with an unsuccessful trial of labor resulting in cesarean delivery because these deliveries have the highest morbidity.” However, the panel concluded that women who undergo TOLAC, regardless of the ultimate mode of delivery, are at decreased risk for maternal mortality compared with women who undergo elective repeat cesarean delivery. The panel also cited low-grade evidence of a shorter hospitalization overall for women attempting TOLAC compared with women undergoing elective repeat cesarean delivery.

In 2022, Fitzpatrick et al. aimed to provide an updated review since the publication of the 2010 NIH consensus panel of the evidence regarding short- and long-term outcomes for women and their children following TOLAC versus elective repeat cesarean delivery. The authors also investigated additional outcomes that were not included in the 2010 review, such as maternal mental health and childhood health problems. The authors identified 47 eligible studies, including 2 randomized controlled trials, 44 cohort studies, and 1 case control study. Since the 2010 review, nine studies reported on maternal mortality. A total of four maternal deaths were reported, all of which occurred in the elective repeat cesarean group. Some 31 studies reported rates of uterine rupture, which varied from 0.00% to 4.8% in the TOLAC group and 0.00% to 2.9% in the elective repeat cesarean group. An increased risk of uterine rupture with TOLAC was reported in 16/31 studies. The risk of rupture was more apparent when labor was induced or augmented. The remaining 15/31 studies found no statistically significant difference between groups, or they reported no uterine ruptures in either group. However, the authors noted that most of these studies were small. Of studies reporting the incidence of hysterectomy, most (12/14) found there was no significant difference in risk between planned mode of delivery.

Outcomes for hemorrhage were more variable, with the authors noting a lack of consistency on the definition of hemorrhage among studies. Overall, the authors identified 18 publications reporting the risk of maternal hemorrhage since the 2010 NIH review. Half of the studies (9/18) found an increased risk of hemorrhage among the TOLAC cohorts (relative risk ranging from 1.25 to 9.90). Only two studies found a reduced risk of hemorrhage among TOLAC patients, and the remaining seven found no risk difference between groups. A comparison of infection rates was also challenging to perform, as the definition criteria for infection varied substantially among studies. However, the absolute risks of infection were nearly identical between groups (TOLAC, 0.02% to 15.7%; elective repeat cesarean, 0.00% to 15.7%). TOLAC was favored for reduced length of hospitalization (5/7 studies) and increased rates of breastfeeding (2/2 studies). Similar to the 2010 NIH panel review, the authors were unable to identify any studies reporting the incidence of urinary or fecal incontinence. The investigators also explored the impact of mode of delivery on maternal mental health, which was not an outcome included in the 2010 review. Only two eligible studies were identified: one small RCT reported no significant risk difference, while a large population cohort study found TOLAC was associated with a 17% reduced risk of the mother being prescribed an antidepressant in the first year after delivery. Ultimately, the authors concluded, “Collectively, the evidence supports existing consensus that there are risks and benefits associated with both planned VBAC and [elective repeat cesarean], and therefore women without contraindications to VBAC should be given an informed choice about planned mode of birth after previous cesarean section.”