Maternal Outcomes

Flamm et al. performed a prospective multicenter study of TOLAC. Of the 7229 patients, 5022 (70%) underwent TOLAC and 2207 underwent elective repeat cesarean delivery. Some 3746 (75%) of the women who opted for TOLAC delivered vaginally. The incidence of uterine rupture was 0.8%. The incidence of postpartum transfusion, the incidence of postpartum fever, and the duration of hospitalization were significantly lower in the TOLAC group than in the elective repeat cesarean group. Likewise, in a 1991 meta-analysis of 31 studies, Rosen et al. noted that maternal febrile morbidity was significantly lower among women who attempted VBAC than among those who underwent elective repeat cesarean delivery.

In contrast, McMahon et al. performed a population-based longitudinal study of 6138 women in Nova Scotia who had previously undergone cesarean delivery and who delivered a single live infant between 1986 and 1992. Some 3249 women attempted VBAC, and 2889 women chose a repeat cesarean delivery. There was no difference between the two groups in the incidence of “minor complications” (e.g., puerperal fever, transfusion, wound infection). However, “major complications” (e.g., hysterectomy, uterine rupture, operative injury) were nearly twice as common among women who attempted VBAC than among women who underwent elective repeat cesarean delivery.

Landon et al. subsequently conducted a prospective 4-year observational study of all parturients with a singleton gestation and a prior cesarean delivery at 19 academic medical centers. Among the 17,898 women who attempted VBAC, 13,139 (73.4%) delivered vaginally. Symptomatic uterine rupture occurred in 124 (0.7%) women who underwent a trial of labor. The rate of endometritis was higher in women who underwent a trial of labor than in women who had an elective repeat cesarean delivery (2.9% versus 1.8%), as was the rate of blood transfusion (1.7% versus 1.0%).

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).

Cahill et al. performed a multicenter cohort study in which they concluded that among TOLAC candidates who had a prior vaginal delivery, those who attempted VBAC had a lower risk for overall major maternal morbidities, as well as maternal fever and transfusion, than women who chose repeat cesarean delivery. These investigators concluded that women who have had a prior vaginal delivery have “less composite maternal morbidity if they attempt VBAC compared with [those] undergoing an elective repeat cesarean delivery.” Further, they concluded that a trial of labor is “a safer overall option for women who have had a prior vaginal birth.”

Rossi and D’Addario performed a meta-analysis 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.

The 2010 NIH consensus development panel noted that 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.

Neonatal Outcomes

Lydon-Rochelle et al. conducted a population-based, retrospective cohort analysis of obstetric outcomes for all 20,095 nulliparous women who gave birth to a live singleton infant by cesarean delivery in civilian hospitals in Washington between 1987 and 1996 and who subsequently delivered a second singleton child during the same period. These investigators observed that spontaneous labor 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). Further, the incidence of infant death was more than 10 times higher among the 91 women who experienced uterine rupture than among the 20,004 who did not (i.e., a 5.5% incidence of infant death versus a 0.5% incidence, respectively).

In the study performed by McMahon et al. there was no difference between the two groups in perinatal mortality or morbidity. However, two perinatal deaths occurred after uterine rupture in the TOLAC group. Landon et al. observed that hypoxic-ischemic encephalopathy occurred in no infants whose mothers underwent elective repeat cesarean delivery and in 12 infants delivered at term whose mothers underwent a trial of labor ( P < .001).

The 2010 NIH consensus development panel concluded that the perinatal mortality rate (death between 20 weeks’ gestation and 28 days of life) is increased with TOLAC when compared with elective repeat cesarean delivery (i.e., 130 deaths per 100,000 infants compared with 50 deaths per 100,000 infants, respectively). Likewise, the panel concluded that the neonatal mortality rate (death in the first 28 days of life) is also increased with TOLAC when compared with elective repeat cesarean delivery (110 deaths per 100,000 infants versus 50 deaths per 100,000 infants, respectively).

On the other hand, elective cesarean delivery results in some cases of iatrogenic neonatal respiratory sequelae, including respiratory distress syndrome and transient tachypnea of the newborn. Kamath et al. observed that newborns born after elective repeat cesarean delivery had significantly higher rates of respiratory morbidity and neonatal intensive care unit admission—and a longer length of hospital stay—than infants whose mothers attempted VBAC. However, the 2010 NIH consensus development panel concluded that there is insufficient evidence to determine whether substantial differences in respiratory outcomes occur in infants born via elective repeat cesarean delivery compared with infants born after TOLAC.

History of More Than One Cesarean Delivery

Studies that have assessed outcomes of TOLAC in women with a history of more than one cesarean delivery have not demonstrated consistent conclusions. 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, when compared with 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 some 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. The ACOG concluded that it is reasonable to consider TOLAC for women with two previous low-transverse cesarean deliveries. In 2015, the RCOG stated that “women who have had two or more prior lower segment caesarean deliveries may be offered VBAC after counselling by a senior obstetrician.” Data regarding the risk for TOLAC in women with more than two previous cesarean deliveries are limited.

Previous Low-Vertical Incision

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.) Naef et al. retrospectively reviewed outcomes for 174 women who attempted VBAC after a previous low-vertical cesarean delivery; 144 (83%) women delivered vaginally. Uterine rupture occurred in 2 (1.1%) of the patients. These investigators concluded that “the likelihood of successful outcome and the incidence of complications are comparable to those of published experience with a trial of labor after a previous low-segment transverse incision.” Adair et al. made similar observations. 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.

Twin Gestation

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. Early reports suggested otherwise, but these studies were 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. Some 120 (64.5%) women delivered vaginally. Women who attempted a trial of labor 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 a trial of labor in women with a twin gestation after previous cesarean delivery does not appear to be associated with a higher risk for maternal morbidity.

Ford et al. subsequently examined outcomes for 6555 women with a twin gestation who delivered between 1993 and 2002. Among 1850 women who underwent a trial of labor, 836 (45.2%) delivered vaginally. The rate of uterine rupture was higher in the trial-of-labor group than in the elective cesarean delivery group (0.9% versus 0.1%), but the rate of wound complications was lower in the trial-of-labor 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.” In contrast, the RCOG stated that “there is uncertainty about the safety and efficacy of planned VBAC in pregnancies complicated by … twin gestation.”

Unknown Uterine Scar

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. At least two studies have concluded that a trial of labor does not significantly increase maternal or perinatal mortality in patients with an unknown uterine scar. Perhaps this conclusion is true because most patients with an unknown uterine scar had a low-transverse uterine incision at 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.”

Suspected Macrosomia

In 1994, the ACOG concluded that an estimated fetal weight of more than 4000 g does not contraindicate TOLAC. However, in 1999, the ACOG included suspected macrosomia on the list of TOLAC eligibility criteria that are controversial. In 2004, the ACOG noted that macrosomia is associated with a lower likelihood of successful VBAC but did not include a specific recommendation regarding TOLAC in cases of suspected macrosomia. However, the ACOG cited one report that observed that the rate of uterine rupture appeared to be higher only in women without a previous vaginal delivery. A report from the Maternal-Fetal Medicine Unit Cesarean Registry concluded that for women with a history of previous cesarean delivery for dystocia, a higher birth weight in a subsequent pregnancy (relative to the first pregnancy birth weight) diminishes the chances of successful VBAC. In 2010, the ACOG concluded that “suspected macrosomia alone should not preclude the possibility of TOLAC.”

Gestation beyond 40 Weeks

Studies have consistently demonstrated decreased rates of successful VBAC in women who undergo TOLAC after 40 weeks’ gestation. One study observed an increased incidence of uterine rupture in women undergoing TOLAC beyond 40 weeks’ gestation, but other studies (including the largest study that has assessed this risk factor) have not confirmed an increased risk for uterine rupture in these patients. The ACOG concluded that although the likelihood of successful VBAC may be diminished in more advanced gestations, a “gestational age greater than 40 weeks alone should not preclude TOLAC.”

Breech Presentation and External Cephalic Version

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 a previous low-transverse uterine incision who are at low risk for adverse maternal and neonatal outcomes from external cephalic version and TOLAC.

Size of Hospital

Most studies of VBAC have been conducted in university or tertiary care hospitals with in-house obstetricians, anesthesia providers, and operating room staff. In 1999, the ACOG noted that “the safety of [a] trial of labor is less well documented in smaller community hospitals or facilities where resources may be more limited.” 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). However, the rates of maternal blood transfusion and composite adverse maternal outcome were identical in community and university hospitals. The ACOG and the Society for Maternal-Fetal Medicine have recommended that attempted VBAC should occur in a level I center or higher.

Contraindications

Contraindications to planned TOLAC include :

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

  
  
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  Previous uterine rupture

  
  
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  Medical or obstetric complication that precludes labor and vaginal delivery

  
  
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  Inability to perform emergency cesarean delivery because of unavailable surgeon, anesthesia provider, or operating room staff

Social and Economic Factors

Why do most eligible patients choose to undergo elective repeat cesarean delivery? The low frequency of TOLAC has resulted, in part, from both physician and patient preference. VBAC requires more physician effort than elective repeat cesarean delivery. In some 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.”

In contrast, after assessing both the direct and indirect costs of VBAC, Clark et al. concluded that “any economic savings for the healthcare system of a policy of trial of labor are at best marginal, even in a tertiary care center with a success rate for vaginal birth after cesarean of 70%.” Further, they stated that “a policy of trial of labor does not result in any cost saving under most birthing circumstances encountered in the United States today.” The ACOG had earlier acknowledged that “the difficulty in assessing the cost-benefit of VBAC is that the costs are not all incurred by one entity.” In 2004, the ACOG made the following conclusion:

A true analysis of the cost-effectiveness of VBAC should include hospital and physician costs, the method of reimbursement, potential professional liability expenses, and the probability that a woman will continue with childbearing after her first attempt at VBAC. Higher costs may be incurred by a hospital if a woman has a prolonged labor or has significant complications or if the newborn is admitted to a neonatal intensive care unit.

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. (A scheduled, elective cesarean delivery allows the patient to arrange for a relative or friend to provide child care.) Kirk et al. questioned 160 women regarding factors affecting their choice between VBAC 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 a trial of labor 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.

Some insurance carriers previously required that eligible women with a history of previous cesarean delivery attempt VBAC in subsequent pregnancies. These carriers denied partial or full reimbursement to women who chose elective repeat cesarean delivery unless there was a medical reason to perform repeat cesarean delivery. The ACOG and others have agreed that hospitals and insurers should not mandate a trial of labor for pregnant women with a history of previous cesarean delivery. In 2004, the ACOG concluded, “After thorough counseling that weighs the individual benefits and risks of VBAC, the ultimate decision to attempt this procedure or undergo a repeat cesarean delivery should be made by the patient and her physician.”

Bernstein et al. found that TOLAC-eligible women undergoing either TOLAC or elective repeat cesarean delivery were not adequately informed about the risks and benefits of the two options, and they also found that provider preference drove the decision regarding the planned mode of delivery. Cox emphasized and discussed the importance of shared decision-making when choosing the mode of delivery after a previous cesarean. It is important to discuss with the patient her family planning goals, as the risk for a morbidly adherent placenta 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 factor into consideration when deciding between TOLAC and repeat cesarean delivery.

Medicolegal Factors

What is the risk for uterine rupture during VBAC? A lower uterine segment scar is relatively avascular, and massive hemorrhage rarely follows separation of a lower segment scar. In contrast, rupture of a classic uterine scar may result in massive intraperitoneal bleeding. Unfortunately, there is some 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.

Some obstetricians have suggested that earlier studies underestimated the risks associated with TOLAC. Scott reported 12 women from Salt Lake City, Utah, who experienced clinically significant uterine rupture during TOLAC. Some of the women did not experience optimal obstetric management. For example, Scott’s series included two women whose labor occurred at home. Of interest, the number of home VBACs in the United States increased from 664 in 2003 to approximately 1000 in 2008, perhaps as a result of restricted access to TOLAC in some hospitals.

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. was an observational study that reflected “broad experience in a wide range of clinical-practice settings,” 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 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 repeated cesarean section.

In an earlier editorial, Pitkin made the following statement regarding VBAC: “Many women with previous cesareans can be delivered vaginally, and thereby gain substantial advantage, but neither the decision for trial [of] labor nor management during that labor should be arrived at in a cavalier or superficial manner.”