Choosing the route of delivery after cesarean birth

INTRODUCTION — Patients who have undergone a previous cesarean birth have the option of proceeding with a trial of labor after cesarean (TOLAC) birth or planned repeat cesarean birth (PRCB) in a subsequent pregnancy. Planned TOLAC may result in labor with vaginal birth (VBAC) or unplanned intrapartum cesarean birth.

Decision-making regarding mode of birth must take into consideration the patient's personal preferences, obstetric history, data on the risks and benefits of TOLAC versus PRCB, and availability of TOLAC in the selected birth setting. Two major concerns that patients have when making this decision are the chance of successful VBAC, which can be estimated with a calculator, and the chance of uterine rupture, which is low in patients with one previous low transverse hysterotomy incision. (Related Pathway(s): Trial of labor after cesarean: Shared decision-making with a pregnant patient during the first prenatal visit.)

This topic will review issues related to choosing the route of birth after cesarean birth, including calculators to predict an individual's likelihood of success. Issues related to management of labor and birth during TOLAC and issues related to repeat cesarean birth are discussed separately. (See "Trial of labor after cesarean birth: Intrapartum management" and "Repeat cesarean birth".)

PREVALENCE — In the United States, the prevalence of attempted TOLAC was 21.7 percent in 2020 [1].

RISKS/BENEFITS OF TOLAC VERSUS PRCB

Overview — The medical and obstetric benefits of successful TOLAC derive from avoidance of the potential adverse outcomes associated with repeat cesarean birth, especially multiple repeat cesarean births. Most maternal morbidity associated with TOLAC occurs when intrapartum cesarean birth becomes necessary, which is associated with increased risks for postoperative infection and other morbidities compared with PRCB. A less common but serious potential adverse outcome associated with TOLAC is uterine rupture, which can be associated with serious morbidity, particularly for the neonate in whom uterine rupture can be fatal.

Conversely, the medical and obstetric benefits of PRCB derive from avoidance of the potential adverse outcomes associated with TOLAC, primarily uterine rupture and morbidity associated with intrapartum cesarean birth. Thus, the benefits of TOLAC are closely related to having a successful vaginal birth, which has lower morbidity than both planned and intrapartum cesarean birth. (See "Cesarean birth: Postoperative care, complications, and long-term sequelae", section on 'Complications' and "Uterine rupture: After previous cesarean birth".)

In 2010, the National Institute of Child Health and Human Development and the Office of Medical Applications of Research of the National Institutes of Health convened a Consensus Development Conference to evaluate all available evidence related to TOLAC and make recommendations for practitioners regarding the management of patients with a prior cesarean birth [2]. Their final report summarized the state of knowledge concerning the outcomes of PRCB versus TOLAC in patients who have undergone one or more prior cesarean births. These findings and subsequent United States data are described throughout this topic.

Large data sets from other countries are also available and report similar findings. As an example, the Canadian Perinatal Surveillance System reported that term TOLAC in Canada between 2003 and 2015 was associated with an increased relative risk, but low absolute rate, of severe maternal morbidity and mortality compared with PRCB (10.7 versus 5.65 per 1000 births; adjusted rate ratio [RR] 1.96, 95% CI 1.76-2.19) [3]. The same was true for neonatal morbidity (seizures, assisted ventilation, continuous positive airway pressure) and mortality (20.8 versus 14.5 per 1000 births; adjusted RR 1.49, 95% CI 1.38-1.61).

Limitations of available evidence — No large randomized trials have been performed to provide comparative data on outcomes of TOLAC versus PRCB; a systematic review identified only two randomized trials involving a total of 320 participants, with minimal data on maternal and newborn clinical outcomes [4].

It is important to recognize that many case-control and cohort studies have compared these two routes of birth. Most of these studies reported maternal and neonatal outcomes based on the actual route of birth rather than the intended route. When this type of analysis is performed, the outcomes of patients who underwent cesarean birth after an unsuccessful TOLAC were grouped along with the outcomes of those who underwent PRCB, which is a less morbid procedure and biases the findings in favor of TOLAC. The outcomes of patients who planned PRCB but spontaneously labored and gave birth vaginally were grouped along with the outcomes of patients who had a successful TOLAC, which also biases findings and leads to misleading conclusions about the actual risk of adverse events or outcomes associated with the decision to attempt TOLAC or PRCB. Analysis of these data is also complicated by imprecise definitions and outcome measurements as well as difficulties encountered when trying to characterize events and outcomes attributable to route of birth.

Although data from randomized trials would be ideal, it would be difficult to recruit adequate numbers of patients willing to consent to randomization to TOLAC versus PRCB. To overcome this problem, a propensity analysis was performed to simulate a randomized trial of TOLAC versus PRCB in patients with one prior cesarean birth [5]. Propensity analyses can provide helpful insights by using statistical techniques to balance the comparison groups; however, they are not a substitute for well-designed randomized trials. This propensity analysis found that the rates of endometritis, operative injury, respiratory distress syndrome, and newborn infection were lower with PRCB, whereas the rates of hysterectomy and wound complication were higher with PRCB. The authors estimated that 62 patients (95% CI 40-138) would need to undergo PRCB to prevent one maternal adverse outcome from TOLAC and 43 patients (95% CI 29-78) would need to undergo PRCB to prevent one neonatal adverse outcome from TOLAC.

Maternal outcomes — The following table summarizes maternal outcomes associated with VBAC and PRCB (table 1); it was derived from a 2010 systematic review of 41 studies [6] and is subject to the limitations discussed above (see 'Limitations of available evidence' above). Selected outcomes are discussed in more detail below.

●Uterine rupture – The incidence of uterine rupture is low (in resource-rich countries), but when it occurs, it is often associated with TOLAC and is potentially life threatening. The National Institute of Child Health and Human Development consensus conference panel described uterine rupture risk in the following way [7], based on data in the 2010 systematic review [6]. Importantly, in this document, uterine rupture was defined anatomically as partial or complete separation of the uterine wall, rather than requiring anatomic separation accompanied by changes in maternal or fetal status.

•In a hypothetical group of 100,000 patients of any gestational age who undergo TOLAC, there will be 468 cases of uterine rupture. Looked at in another way, approximately 1 in 200 TOLACs will lead to uterine rupture.

•In a hypothetical group of 100,000 patients of any gestational age who undergo PRCB, there will be 26 uterine ruptures.

•The types and frequencies of major maternal and neonatal outcomes of uterine rupture would include:

-Hysterectomy: 14 to 33 percent

-Maternal death: none

-Perinatal death: 0 to 2.8 percent

The risk of rupture is higher (over 1 percent) after ≥2 prior cesareans, with induction of labor, or after a short interdelivery interval. (See "Uterine rupture: After previous cesarean birth".)

●Infection – Although the overall risk of maternal infection appears to be similar for TOLAC and PRCB [6], specific risks vary by clinical setting. For example, only patients in labor are at risk for intrapartum chorioamnionitis. VBAC has a lower frequency of postpartum infection than PRCB, while intrapartum cesarean birth has the highest frequency of postpartum infection [8]. (See "Clinical chorioamnionitis" and "Postpartum endometritis" and "Cesarean birth: Postoperative care, complications, and long-term sequelae", section on 'Complications'.)

●Peripartum hysterectomy – Although some peripartum hysterectomies are performed because of uterine rupture during TOLAC, many others are performed because of placental attachment disorders, which are associated with prior cesarean birth: An increasing number of cesarean births increases the risk for placenta previa and, in turn, the placenta accreta spectrum (table 2). (See "Placenta accreta spectrum: Clinical features, diagnosis, and potential consequences", section on 'Risk factors'.)

●Pelvic floor disorders – Pregnancy itself is a risk factor for future pelvic relaxation disorders. Most available evidence suggests that vaginal birth is more important than exposure to labor on the development of pelvic floor disorders later in life. Although PRCB avoids the potential risks and sequelae of pelvic trauma related to vaginal birth, the absolute benefit compared with TOLAC is unclear and does not appear to outweigh the risks of PRCB. (See "Effect of pregnancy and childbirth on urinary incontinence and pelvic organ prolapse".)

●Convenience – For many patients, a benefit of PRCB is that scheduled birth allows them and their family/friends the ability to make specific work-life plans for the birth and postpartum period. Although induction of labor in patients undergoing TOLAC can also be scheduled, awaiting spontaneous labor is preferred given some studies demonstrating an association between induction and uterine rupture.

Personal benefits of VBAC include shorter hospital stay and quicker return to normal activities compared with PRCB.

●Postpartum permanent contraception – Postpartum permanent contraception (also called sterilization) is readily accomplished at cesarean birth; however, this is a minor advantage of PRCB since the procedure can be performed after a vaginal birth and often immediately following the birth. (See "Postpartum permanent contraception: Procedures".)

Neonatal outcomes — Data regarding the short- and long-term neonatal outcomes after TOLAC versus PRCB are limited and subject to the limitations discussed above (see 'Limitations of available evidence' above) [2]. The 2010 systematic review of 41 studies discussed above reported the following neonatal outcomes related to TOLAC and PRCB [6]:

●Perinatal mortality and neonatal mortality – Perinatal mortality and neonatal mortality rates were higher for TOLAC than for PRCB (perinatal mortality rate: 0.13 versus 0.05 percent; neonatal mortality rate: 0.11 versus 0.06 percent), although the absolute risk is very low.

●Transient tachypnea of the newborn – Transient tachypnea of the newborn was more common with PRCB compared with TOLAC (4.2 versus 3.6 percent). However, neonatal bag and mask ventilation was used more often in neonates born following TOLAC than in those born following PRCB (5.4 versus 2.5 percent).

●Other – Data were insufficient to determine the direction of risk for hypoxic-ischemic encephalopathy, sepsis, trauma, neonatal intensive care unit (NICU) admission, and adverse neurologic outcomes. However, subsequent studies have reported that the rates of suspected and proven neonatal sepsis are higher for TOLAC than PRCB (suspected sepsis 5 versus 2 percent; proven sepsis 1 versus 0 percent) [9] and reported an increased risk of neonatal depression and NICU admission for TOLAC versus PRCB [10,11].

FACILITY RESOURCES FOR OFFERING TOLAC — The American College of Obstetricians and Gynecologists (ACOG) recommends conducting TOLAC in facilities that are able to perform an emergency cesarean birth in the event of a situation that is an immediate threat to the life of the pregnant patient or fetus [12]. ACOG emphasized that this recommendation was not intended to restrict access to TOLAC and recognized the difficulty of providing this type of care, especially in rural settings. The resources necessary to perform emergency cesarean birth are described separately. (See "Trial of labor after cesarean birth: Intrapartum management", section on 'Facility resources'.)

When resources needed for emergency cesarean birth are limited, ACOG recommends that practitioners discuss the available resources at the planned birth facility with patients who are considering TOLAC. After this discussion, some patients may consider an alternative birth site that has resources for performing an emergency cesarean birth and providing the required neonatal care in the event of complications, some may tolerate higher levels of risk in order to pursue TOLAC at their preferred birth facility, and some may choose PRCB. A decision to plan for TOLAC in a setting lacking resources to perform an emergency cesarean birth should be made only after careful consideration by the patient and their health care provider. In such instances, the discussion and plan should be documented in the obstetric record. Discussion of birth options early in pregnancy can facilitate transfer of care if desired by the patient and practitioner.

We agree with ACOG that TOLAC should not be attempted as a home birth.

FACTORS TO CONSIDER IN PATIENT-CENTERED DECISION-MAKING — The decision for a TOLAC or PRCB is made by the patient in collaboration with their provider. The discussion should begin early in the course of prenatal care and may even begin before conception. Ongoing discussion throughout pregnancy is important as conditions may arise that alter the balance of risks and benefits of the planned route of birth. Whenever possible, clinicians should comply with the patient's preference [2,7].

This decision should be based upon the best available clinical evidence and involves a combination of factors, including:

●Availability of TOLAC at the planned birth setting (see 'Facility resources for offering TOLAC' above)

●Probability of VBAC (see 'Predicting the probability of VBAC' below)

•A cross-sectional analysis of over 4 million singleton, cephalic, term births in individuals with a history of one or two cesarean births in the National Vital Statistics System reported the rate of successful TOLAC increased from 69.8 percent in 2010 to 74.7 percent in 2020 [1].

Success rates vary among institutions and providers and are affected by antepartum, intrapartum, and nonmedical factors [7]. Factors known to affect TOLAC success rates and the individual patient's probability of success obviously need to be addressed in person-centered decision-making.

•In a 2010 meta-analysis, the two factors that increased the odds of VBAC by at least threefold were history of VBAC and history of vaginal birth [13]. The most important factor associated with failed TOLAC (ie, intrapartum cesarean birth) was a prior cesarean birth for a recurring indication, such as failure to progress. Other factors that played a role, but were not as strongly associated with failed TOLAC, were increasing body mass index and older maternal age. Induction of labor significantly reduced the odds of VBAC compared with entering labor spontaneously, but a better control group would have been patients who were managed expectantly. (See 'Predicting the probability of VBAC' below.)

●Benefits and significance and estimated frequency of complications with TOLAC and PRCB, including individual patient factors that affect the risks and benefits for each birth route (see 'Risks/benefits of TOLAC versus PRCB' above) and individual patient factors that impact the risk of uterine rupture. (See 'Candidates for TOLAC' below.)

Unlike most medical decisions, where patients are comparing risks and benefits for themselves, the pregnant patient must compare risks and benefits for both themself and their fetus, and the risks and benefits for these two individuals sometimes do not align: A decision that reduces maternal risk may be associated with increased fetal risk and vice versa. It should be noted that most pregnant patients are willing to tolerate a high degree of risk to themselves in exchange for zero or near-zero risk for their child [14,15]. However, a strong maternal desire to achieve a birth via out-of-hospital TOLAC increases risk to both mother and child [16-19].

●Personal values, preferences, past birthing experiences, and future pregnancy plans. A patient's decision regarding route of birth is influenced by factors other than the VBAC rate and risk of uterine rupture.

Common reasons patients choose TOLAC include [2,7,20,21]:

•Future pregnancy plans since multiple cesarean births increase the risk for placenta previa and accreta spectrum

•Family obligations that make a speedy return to normal activities postpartum desirable

•Desire to experience labor and vaginal birth

•Desire for their partners' greater involvement in labor and birth

Common reasons patients choose PRCB include:

•Scheduling convenience

•Ease of arranging a procedure for permanent contraception at the time of birth

•Fear of failed trial of labor and emergency cesarean birth

•Avoidance of labor pain and labor in general

•Hospital policies restricting access to TOLAC

In addition, patients report that their health care providers' recommendations and preferences exert a strong influence on their decision of whether or not to pursue TOLAC [22]. They are also influenced by the opinion of the person, other than their provider, whose opinion matters most to them [21].

CANDIDATES FOR TOLAC

Optimal candidates — The ideal candidates for TOLAC are patients with a high likelihood of VBAC and a very low likelihood of intrapartum uterine rupture.

One prior low transverse uterine incision — Practitioners should obtain operative reports from prior cesarean births to document the location of the hysterotomy. There is good and consistent evidence that a patient who has undergone only one previous cesarean birth via a low transverse hysterotomy incision has the lowest risk of uterine scar separation during a subsequent trial of labor; thus, TOLAC is a reasonably safe option for these patients [2,7]. In this setting, the body of evidence suggests a VBAC rate of 60 to 80 percent [23], with an estimated uterine rupture rate of 0.4 to 0.7 percent [7,24].

Other potential candidates

Prior low vertical uterine incision — As discussed above, practitioners should obtain operative reports from prior cesarean births to determine whether a vertical uterine incision was performed and its upper extent. If it extended into the contractile (upper) portion of the uterus, the patient should be managed as if they had a prior classical hysterotomy and is not an appropriate candidate for TOLAC. (See 'Prior transfundal uterine incision' below.)

If the incision did not extend into the contractile portion of the uterus, we and the American College of Obstetricians and Gynecologists (ACOG) suggest that the provider discuss the available data on uterine rupture with the patient and together they may reasonably choose to proceed with TOLAC [12]. Although a literature review reported that the frequency of rupture for low vertical uterine incisions ranged from 1.05 to 2.0 percent versus 0.4 to 0.7 percent for low transverse uterine incisions [23], the evidence was inconclusive due to study limitations and inconsistency among the studies.

Two prior low transverse uterine incisions — We and ACOG consider patients with two prior cesarean births to be acceptable candidates for TOLAC, with individualized counseling that accounts for other factors that predict the likelihood of success [12]. (See 'VBAC calculators' below.)

The likelihood of VBAC appears to be similar for patients with one versus two prior cesarean births (65 to 85 percent) [25-28]; however, patients with more than one prior cesarean may have a slightly higher rate of uterine rupture. In a 2010 meta-analysis of five cohort studies of uterine rupture in patients with prior cesarean births, those undergoing TOLAC after one prior cesarean were at significantly lower risk of rupture than patients with two prior cesareans (0.72 versus 1.59 percent, odds ratio [OR] 0.42, 95% CI 0.29-0.60); however, the definition of rupture varied among studies [29].

Three prior low transverse uterine incisions — Individual counseling, which incorporates future childbearing desires and likelihood of successful VBAC, is important in counseling patients with three or more prior cesarean births; however, only sparse data are available. In one retrospective cohort study, 89 patients with three or more prior cesarean births underwent TOLAC; patients in this study were as likely to have a successful VBAC as those with one prior cesarean and did not experience higher composite maternal morbidity (uterine rupture, bowel or bladder injury, or uterine artery laceration) [30]. Despite the lack of data, it is reasonable to assume an increased risk of uterine rupture with increasing number of prior cesarean births, but the magnitude of risk is not well quantified.

Unknown type of uterine incision — The prior incision type is not always available when caring for a patient in their subsequent pregnancy. Because most patients with a prior uterine incision for common obstetric indications have had a low transverse hysterotomy, we and ACOG believe that decision-making regarding TOLAC versus PRCB can often be based upon this assumption [12]. This conclusion is supported by data from two large studies that found patients who had an unknown type of prior incision had a similar rate of uterine rupture as those with a known prior low transverse uterine incision [8,31]. As an example, uterine rupture occurred in 0.5 percent of patients with an unknown scar type and 0.7 percent of patients with a known low transverse uterine incision in the National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units (MFMU) Network study [8].

Importantly, TOLAC should not be pursued if the incision type is unknown and there is a high clinical suspicion that a prior uterine incision was made into the upper (contractile) segment of the uterus, such as when a cesarean is performed before approximately 28 weeks or in the setting of known lower uterine segment pathology (eg, large leiomyoma). It also should not be pursued if the patient was told that they are not a candidate for TOLAC in the future by the clinician performing the cesarean. As an example, a prospective study observed that over one-third of patients who underwent cesarean birth before 26 weeks had a classical hysterotomy (34.9 compared with 7.8 percent at ≥26 weeks) [32].

Short interpregnancy interval — Delaying conception for at least 18 months following a cesarean birth may be important to allow for adequate healing of the hysterotomy among patients planning a TOLAC; shorter interpregnancy intervals [33], most strikingly <6 months [34], have been associated with an increased risk for uterine rupture during TOLAC. The absolute risk of uterine rupture with interpregnancy intervals <6 months appears to be on the order of 2 to 3 percent [34]. This risk should be considered as part of person-centered decision-making when patients with a short-interpregnancy interval are considering route of birth after cesarean birth. (See "Interpregnancy interval: Optimizing time between pregnancies", section on 'After a cesarean birth'.)

Pregnancy more than 40 weeks of gestation — Although studies have consistently observed that patients who attempt TOLAC beyond 40 weeks of gestation are less likely to have a VBAC [2,35,36], we and ACOG do not consider this gestational age a contraindication to TOLAC [12].

A large retrospective cohort study including over 11,500 patients delivering by TOLAC at both community and tertiary centers found similar rates of uterine rupture in those who delivered <40 and ≥40 weeks of gestation (1.0 and 1.1 percent, respectively) [36]; however, at least two reports with a total of approximately 4100 patients described a higher risk of uterine rupture with TOLAC after 40 weeks (2 to 3 percent) [37,38].

We recommend not performing induction at 39 weeks for the sole purpose of avoiding TOLAC after 40 weeks. In a large study including over 12,600 patients, although induction at 39 weeks was associated with a higher VBAC rate than expectant management (74 versus 61 percent), the risk of uterine rupture was also higher (1.4 versus 0.5 percent) [39].

Twin gestation — We agree with ACOG that patients with twin pregnancies and one previous low transverse cesarean birth are candidates for TOLAC if they have no contraindications to vaginal birth [40]. While most studies report that patients with a twin gestation are significantly less likely to pursue TOLAC, the overall success rate and risk of uterine rupture in this population appears to be similar to that in singleton gestations undergoing TOLAC.

In a meta-analysis of 10 studies examining outcomes of individuals attempting TOLAC with a twin gestation (2336 TOLAC cases and 5763 PRCD cases), the pooled success rate was 72.2 percent (95% CI 59.7-83.2) and the rate of uterine rupture was 0.87 percent (95% CI 0.51-1.31) [41]. In a subsequent retrospective multicenter cohort of 236 twin gestations with cephalic first twin undergoing TOLAC, the VBAC rate was 78 percent and the uterine rupture rate was 0.8 percent [42]. (See "Twin pregnancy: Labor and delivery", section on 'Trial of labor after previous cesarean birth'.)

Macrosomia — We agree with ACOG that suspected fetal macrosomia (estimated fetal weight ≥4000 g) alone should not preclude the option of TOLAC [12,43]. In addition to usual factors, clinicians should consider past birth weight(s) and outcomes and the predicted birth weight in the current pregnancy when assessing risks of TOLAC and probability of VBAC.

For patients with no previous vaginal birth, the likelihood of VBAC falls to ≤50 percent when birth weight increases above 4000 g [44,45]. In one study of TOLAC among such patients, newborn birth weights <4000 g, 4000 to 4249 g, 4250 to 4500 g, and >4500 g were associated with VBAC in 68, 52, 45, and 38 percent of cases, respectively [44]. Success rates were lower if the indication for the previous cesarean birth was cephalopelvic disproportion, failure to progress, or if the patient required either induction or augmentation of labor during TOLAC. In contrast, patients who had a previous vaginal birth had a ≥63 percent rate of VBAC for any of the birth weight strata.

It also should be noted that patients attempting TOLAC with no prior vaginal birth and/or newborn birth weight >4000 g may have a higher likelihood of adverse obstetric outcomes, such as uterine rupture [44,46,47]. In one study, such patients had a 3.6 percent rate of rupture [44]. Notably, the overall uterine rupture rate in this study was 1.4 percent, which exceeds that in the majority of large cohort studies and may reflect ascertainment of uterine rupture through diagnostic codes rather than chart abstraction. Thus, this reported rate should be considered as part of decision-making regarding TOLAC rather than utilized as a quoted probability of uterine rupture in direct patient counseling.

Outside of the setting of TOLAC, ACOG guidelines consider cesarean birth appropriate when the estimated fetal weight is ≥5000 g in patients without diabetes and ≥4500 g in patients with diabetes [43].

Patients with obesity — We agree with ACOG that patients with a body mass index (BMI) ≥30 kg/m² are potential candidates for TOLAC after consideration of the effects of individual characteristics, such as a prior vaginal birth, on probability of VBAC and risks associated with PRCB versus TOLAC [12]. We do not have a specific limitation related to BMI and recognize that patients with obesity may require more time to achieve vaginal birth. (See "Obesity in pregnancy: Complications and maternal management", section on 'Progress of labor'.)

Observational studies have consistently reported that TOLAC is less likely to result in VBAC in patients with obesity [7,48-55]. The largest of these studies was a prospective multicenter study including 6413 obese (BMI 30 to 39.9 kg/m²) and 1638 severely obese (BMI ≥40 kg/m²) patients [51]. The rate of failed trial of labor was 15 percent in patients with BMIs in the normal range, 30 percent in patients with obesity, and 39 percent in patients with severe obesity. The rate of uterine dehiscence/rupture for the three groups was 0.9, 1.4, and 2.1 percent, respectively.

No guidelines have addressed whether TOLAC should be avoided in patients with severe obesity or at any threshold BMI. A secondary analysis of MFMU Cesarean Registry data suggests that patients with obesity undergoing TOLAC are more likely to undergo repeat cesarean during the latent phase despite receiving higher doses of oxytocin and a longer interval to achieve active labor [56].

Maternal diabetes — In our opinion, gestational and pregestational (preexisting) diabetes are not contraindications to TOLAC. We counsel patients with these disorders that the overall rate of VBAC appears to be lower in patients with diabetes compared with nondiabetic patients undergoing TOLAC [50,57,58]; we discuss the potential for shoulder dystocia, especially in the setting of macrosomia; and we consider their past birth history in assessing both their probability of VBAC and shoulder dystocia. (See "Shoulder dystocia: Risk factors and planning birth of high-risk pregnancies".)

Outside of the setting of TOLAC, ACOG considers cesarean birth appropriate when the estimated fetal weight is ≥4500 g in patients with diabetes [43]. ACOG has not addressed the specific issue of TOLAC in patients with diabetes.

Prior one- versus two-layer uterine closure — We generally do not take the technique of prior hysterotomy closure into consideration when counseling patients about TOLAC. A retrospective cohort study of 7683 patients attempting TOLAC using Danish birth registry data found no association between single-layer closure and uterine rupture when compared with double-layer closure (OR 1.17, 95% CI 0.78-1.76) [59]. These findings are consistent with a prior meta-analysis (nine studies, 5810 participants) that also demonstrated no association [60]. However, observational studies have inherent biases, and most are underpowered for the outcome of uterine rupture. Long-term follow-up data from patients enrolled in randomized trials are needed.

ACOG has not addressed the specific issue of prior one- versus two-layer closure when considering whether a woman is an appropriate candidate for TOLAC.

Inappropriate candidates — TOLAC is not an option for patients with standard contraindications to labor or vaginal birth, such as placenta previa. We agree with ACOG that the high risk of intrapartum uterine rupture during TOLAC favors PRCB in patients with [12]:

●Prior transfundal uterine incision

●Prior uterine rupture

Prior transfundal uterine incision — TOLAC is not a reasonably safe option for patients with a prior transfundal uterine incision, and we do not offer TOLAC to these patients. A transfundal uterine incision may have been made at a prior cesarean birth, during a gynecologic surgical procedure (eg, myomectomy, uterine reconstruction because of congenital uterine anomaly), or to gain access to the fetus for a surgical procedure. Timing of PRCB in these settings is reviewed separately. (See "Repeat cesarean birth", section on 'Timing'.)

●Classical, T, or J incisions at cesarean birth – In a literature review, the frequency of rupture for classical or T-shaped incisions ranged from 4 to 9 percent, which is at least twofold higher than the upper estimate of rupture risk for low vertical incisions and more than fivefold higher than the upper estimate of rupture risk for low transverse uterine incisions [23].

The best available data derive from a large, prospective, multicenter, NICHD MFMU Network study of TOLAC that evaluated the outcome of patients with prior classical or either inverted T or J incision who presented in advanced labor or declined repeat cesarean birth [8]. The uterine rupture rate was lower than expected in this study, 1.9 percent, but still unacceptably high.

●Transmyometrial incisions for open fetal surgery – In a retrospective study of reproductive outcomes in subsequent pregnancies after a pregnancy in which open fetal surgery was performed, 14 percent had a uterine dehiscence and another 14 percent had a uterine rupture [61], making the risk of rupture unacceptably high.

●Transmyometrial incisions to resect leiomyomas – The risk of rupture may be increased if the uterine cavity was entered or nearly entered during a prior myomectomy or a large number of myomas were removed. Although the overall quality of this evidence is low, the risk of rupture in these patients is likely unacceptably high. (See "Uterine fibroids (leiomyomas): Issues in pregnancy", section on 'Patients with prior myomectomy'.)

Prior uterine rupture or dehiscence — TOLAC is not a reasonably safe option for patients with a prior uterine rupture, and we do not offer TOLAC to these patients. Patients who have experienced a previous uterine rupture confined to the lower uterine segment are reported to have a high incidence (6 percent) of recurrent uterine rupture with labor [62-66]. Those in whom the prior rupture involved the upper uterine segment have experienced a repeat rupture rate as high as 32 percent [62]. In a 25-year literature review, 22 patients identified to have uterine rupture subsequently became pregnant again [65]. Twenty underwent PRCB at term; the other two patients died following catastrophic uterine rupture at 32 and 35 weeks of gestation. As above, although the overall quality of this evidence is low, the risk of rupture in these patients is likely unacceptably high. (See "Uterine rupture: After previous cesarean birth", section on 'Recurrence risk' and "Uterine rupture: After previous cesarean birth", section on 'Management of subsequent pregnancies'.)

We also do not offer TOLAC to patients with a prior uterine dehiscence, given the limitations of available data, particularly the lack of consistent definitions for rupture versus dehiscence and the lack of consistency in distinguishing catastrophic rupture from benign rupture or dehiscence. The likelihood of subsequent uterine rupture with potential catastrophic outcome is unclear. ACOG has not made specific recommendations for the management of patients with dehiscence and does not distinguish between patients with dehiscence and those with rupture in its TOLAC guideline [12].

Timing of PRCB in these settings is reviewed separately. (See "Repeat cesarean birth", section on 'Timing'.)

Special populations and other considerations

Stillbirth — The balance of risks and benefits is different in the setting of stillbirth since PRCB has no fetal/neonatal benefit. Decision-making on the route of birth in these cases is reviewed separately. (See "Stillbirth: Maternal care".)

Thin lower uterine segment — We do not measure uterine scar thickness because no myometrial thickness threshold value performs sufficiently well to use in clinical practice to predict whether a hysterotomy scar will rupture or remain intact. Studies on use of imaging techniques to predict patients at increased risk of uterine rupture during TOLAC have had mixed results and are reviewed separately. (See "Uterine rupture: After previous cesarean birth", section on 'Antepartum imaging of the hysterotomy scar'.)

Breech presentation — Prior low transverse cesarean birth is not a contraindication to external cephalic version, but version may be less useful in this population. In a meta-analysis of eight studies, the rate of successful external cephalic version in individuals with a prior cesarean birth was 74 percent (interquartile range 63-81%), which was similar to those without a prior cesarean birth [67]. However, individuals with a history of cesarean birth were less likely to ultimately have a successful vaginal birth than those without a history of cesarean (pooled odds ratio [OR] 0.26, 95% CI 0.14-0.50). (See "External cephalic version", section on 'Unlikely or controversial factors'.)

PREDICTING THE PROBABILITY OF VBAC

Our approach — In the author's practice, patients with a previous cesarean birth and a history of vaginal birth (either prior vaginal birth or VBAC) are encouraged to undertake a TOLAC (assuming no contraindications), given that the VBAC rate has been reported to be as high as 83 percent for patients with a previous vaginal birth and 94 percent for those with a previous VBAC [13].

For patients outside of this small subset of the population, the author frequently uses a VBAC calculator to inform them of their individual chance of achieving a vaginal birth (see 'VBAC calculators' below). This can be enlightening for patients who are unaware that they have a good chance of achieving a vaginal birth after their previous cesarean. Many good candidates for TOLAC choose PRCB, possibly because of lack of awareness of their chance of VBAC and the relative risks of each approach [68].

The following observational data suggest that the morbidities of TOLAC and PRCB are equivalent when the predicted chance of VBAC is >60 to 70 percent, but higher with TOLAC when the predicted chance of VBAC is <60 to 70 percent [69,70]; no randomized trials have been performed.

●A prospective cohort study including over 13,500 patients eligible for TOLAC compared rates of major morbidity (hysterectomy or operative injury) and minor morbidity (puerperal fever, blood transfusion, abdominal wound infection) in patients undergoing PRCB with patients undergoing TOLAC, stratified by their likelihood of VBAC using the Maternal-Fetal Medicine Units (MFMU) Network at entry to prenatal care calculator [69]. Patients with >70 percent likelihood of VBAC had maternal morbidity similar to those undergoing PRCB (relative risk [RR] 0.80, 95% CI 0.5-1.2), while those with a calculated likelihood of VBAC <70 percent had an increased risk of maternal morbidity (RR 2.2, 95% CI 1.5-3.1).

●In a retrospective cohort study of 8505 patients eligible for TOLAC, maternal morbidity in the TOLAC group was similar to that in the PRCB group when the predicted probability of VBAC was ≥60 percent (RR 0.8, 95% CI 0.6-1.1) but was higher than the PRCB group when the predicted probability of VBAC was <60 percent (RR 2.3, 95% CI 1.4-4.0) [70]. Neonatal morbidity was similar between groups when the probability of VBAC was ≥70 percent (RR 1.2, 95% CI 0.9-1.5).

Neither study's composite maternal morbidity outcome included obstetric anal sphincter injury (OASIS), which appears to be increased in patients undergoing TOLAC compared with nulliparous patients undergoing a first vaginal birth [71-74]. Risk factors for OASIS are reviewed separately. (See "Obstetric anal sphincter injury (OASIS)", section on 'Epidemiology and risk factors'.)

The author uses the MFMU Network at entry to prenatal care calculator (see 'MFMU Network calculator for use at entry to prenatal care' below) to help patients begin to make decisions regarding their planned birth route [75]. The calculated predicted probability of VBAC is documented in the medical record but does not replace documentation of the complete counseling session, including the risks and benefits associated with a TOLAC. Other clinical factors that are discussed with some patients, as clinically appropriate, include specific circumstances of the prior cesarean birth, anticipated size of this infant, desire for future childbearing, and other individual level factors that may influence the chance of success.

The author does not use VBAC calculator results to strongly discourage a motivated patient from pursuing a TOLAC, given the poor negative predictive value of existing models. Many patients with a low predicted probability of vaginal birth using a VBAC calculator will still give birth vaginally [13].

Patients who are good candidates for TOLAC but desire a repeat cesarean birth are encouraged to keep an open mind. If these patients present in spontaneous labor prior to their scheduled cesarean birth or are undecided at admission to the labor unit, the possibility of TOLAC can be readdressed.

VBAC calculators — Both clinicians and patients typically desire individualized information about (1) the chance of VBAC and (2) the balance between the risks of maternal or fetal morbidity with TOLAC compared with PRCB. Many calculators have been created to assist patients in better understanding their individual chance of success.

The goal of TOLAC calculators and models is to predict an individual's chance of VBAC based on their demographic and clinical risk factors [48,76-80]. The probability of VBAC is not only important as a direct measure of outcome, but also as an indirect measure of maternal morbidity: Major maternal morbidity is lowest in patients who have VBAC (morbidity 0.2 percent), higher in patients who undergo PRCB (morbidity 0.8 percent), and highest in patients who have a repeat cesarean birth after a failed TOLAC (morbidity 3.8 percent) [81].

Although a TOLAC calculator or model can predict the probability of vaginal birth, which is a key concern of patients contemplating TOLAC versus PRCB, a variety of other factors also influence a patient's decision regarding route of birth. These factors are not addressed by calculators and are discussed above. (See 'Factors to consider in patient-centered decision-making' above.)

The calculator discussed in this topic was chosen because it is widely used in practice and was developed using a multivariable logistic regression model. However, the calculator has several limitations, including [82,83]:

●No calculator has been prospectively validated to determine whether utilization of the calculator actually reduces maternal morbidity

●No calculator has been validated in patients with multiple gestations

●No calculator predicts patient-specific morbidity rates, such as risk of uterine rupture

MFMU Network calculator for use at entry to prenatal care — The MFMU website provides a VBAC calculator at no cost that predicts the chance of VBAC based on information available at the first prenatal visit [75]. The calculator includes fields for maternal age, height, weight, and prepregnancy body mass index (BMI), obstetric history (no prior vaginal birth, prior vaginal birth only before cesarean, prior VBAC), prior cesarean for arrest (ie, a potentially recurring indication for cesarean birth), and treatment for hypertension (yes/no).

The MFMU Network entry to prenatal care calculator was originally created using a multivariable logistic regression model in a prospective cohort of patients undergoing a trial of labor with a term singleton fetus in cephalic presentation after one prior low transverse cesarean birth [48]. Of the study population of 11,856 patients, 73 percent gave birth vaginally. The overall predictive capability of the model was fair to good, with an area under the curve (AUC) of 0.75 (95% CI 0.74-0.77). (A Receiver Operating Characteristic curve plots true positives against false positives; a test with AUC 0.5 is equivalent to a coin toss whereas AUC 1.0 accurately discriminates between true positives and false positives.) The best performance was in patients with a predicted probability of vaginal birth greater than 35 percent. The nomogram was internally validated with a subset of the initial study population [48] and several independent retrospective cohorts [84-88] of patients with one or two prior cesarean births [25].

In 2021, the MFMU Network entry to prenatal care calculator was updated to exclude race and ethnicity [75]. The updated calculator has a similar AUC to the original calculator of 0.75 (95% CI 0.74-0.77). The factors predictive of VBAC were taller maternal height and a history of vaginal birth, particularly having a history of VBAC. Similar to other analyses, patients with a recurrent indication for cesarean, including arrest of descent and arrest of dilation, were less likely to have a VBAC. Patients of older age, higher weight, and those who were being treated with medications for chronic hypertension were also less likely to have a VBAC. This new model has not yet been validated in other populations.

Although the MFMU Network prenatal care prediction nomogram is useful for identifying patients who are either excellent or very poor candidates for TOLAC, it does not incorporate factors that arise later in gestation that are known to influence the probability of VBAC.

An UpToDate calculator (calculator 1) for predicting the probability of VBAC in patients at presentation for prenatal care is also available, based on the same source as the MFMU calculator and yielding the same results.

Calculators for use at admission for birth — Calculators designed to be used close to delivery may better predict TOLAC success than early pregnancy calculators since they incorporate variables such as cervical examination and ultrasound findings such as estimated fetal weight, head-perineum distance, posterior cervical angle. and residual myometrial thickness. However, many lack external validation and are at high risk of bias [89].

The MFMU Network website previously provided a VBAC calculator that predicted the chance of VBAC based on information available at the time of admission for birth [90]. This calculator, which included race and ethnicity, is no longer available, in acknowledgement that the association between race or ethnicity and VBAC success rates is not based on biologic evidence and is likely explained by other variables.

Person-centered decision-making model — Our person-centered decision-making model for choosing mode of birth in patients with a history of cesarean birth uses an existing VBAC calculator as part of the decision-making process (algorithm 1). It has been hypothesized that the number of patients eligible for TOLAC who opt for it rather than PRCB could be increased with use of a decision support tool that provides accurate information regarding the process and potential outcomes of both modes of birth, an individualized assessment of their likelihood of successful VBAC, and consideration of their values and preferences. However, the first large randomized trial (PROCEED) of a well-designed, person-centered decision support tool did not raise the TOLAC rate compared with usual care (TOLAC rate 43.3 versus 46.2 percent) [91]. The multicenter trial included 1485 patients less than 25 weeks with one prior cesarean birth and no contraindication to TOLAC. It is possible that usual care in the academic centers where the trial was conducted was highly effective, and the tool might be more useful in other settings. In this trial, both groups had low decisional conflict, similar knowledge, high decision self-efficacy, and high decisional satisfaction, which indicated similar decision quality.

Another multicenter, cluster randomized trial (PRISMA) examined a two-year multifaceted intervention to reduce perinatal morbidity for patients with one prior cesarean birth [92]. The trial was conducted at 40 hospitals in Quebec and included over 10,000 patients in each of the intervention and usual care (control) groups. The multifaceted intervention included patient-centered decision support, use of a calculator to estimate the likelihood of VBAC, sonographic assessment of the thickness of the lower uterine segment between 35+0 and 38+6 weeks to estimate the risk of uterine rupture, and clinician training in best practices for intrapartum care of patients attempting TOLAC [48,80]. Major findings were:

●The intervention resulted in a reduction in composite perinatal morbidity from baseline (aOR for incremental change over time 0.72, 95% CI 0.52-0.99; adjusted absolute risk difference -1.2 percent). The composite outcome consisted of perinatal death without lethal anomalies, Apgar score at five minutes <4, metabolic acidosis, major trauma, intracerebral or intraventricular hemorrhage grade 3 and 4, periventricular leukomalacia, hypoxic-ischemic encephalopathy, seizure, invasive mechanical ventilation, major respiratory morbidity, necrotizing enterocolitis, proven neonatal sepsis or infection, and hypotension requiring vasopressor support.

The reduction in composite perinatal morbidity was driven primarily by differences in the rates of metabolic acidosis (pH <7.0 and base excess ≤-12 mmol/L) and major trauma (skull fracture, subdural or subarachnoid hemorrhage, brachial plexus injury, spinal cord injury, major genital injury, paralysis at discharge).

●Rates of PRCB, TOLAC, intrapartum cesarean birth, VBAC, and uterine rupture were not significantly different between groups.

●The intervention resulted in a reduction in composite major maternal morbidity compared with the control group (aOR 0.54, 95% CI 0.33-0.89; adjusted absolute risk difference -1.1 percent). Major morbidity included death, hysterectomy, thromboembolism, admission to intensive care unit for ≥4 days, acute pulmonary edema, cardiogenic shock, septicemia, injury or lacerations to internal organs requiring surgical repair, and uterine rupture. The reduction in the composite was mostly due to a reduction in internal organ injuries.

The multi-faceted intervention precludes identification of the component(s) resulting in improved outcomes. Further assessment of the components of this intervention in different patient populations is warranted and would help practitioners better understand how to incorporate these findings into practice. Clinician training in best practices for intrapartum care may be the most helpful, given the reduction in rates of neonatal metabolic acidosis and trauma.

Model for preterm pregnancies — Only one model predicts the likelihood of VBAC in patients who are giving birth preterm. This model was created from an existing prospectively collected cohort of 1295 patients undergoing TOLAC between 26+0 and 36+6 weeks of gestation and had an overall VBAC rate of 76.6 percent [93]. Factors associated with increased likelihood of VBAC were diabetes, greater cervical dilation, history of vaginal birth, and history of VBAC. Factors associated with a decreased likelihood of VBAC were induction of labor, recurring indication for prior cesarean, and hypertensive disease. The overall predictive capability of the model was very good with an AUC of 0.80 (95% CI 0.77-0.83). The lengthy logistic regression equation used to calculate the likelihood of VBAC is not useful as a point-of-care resource but is available at the end of the publication.

COST-EFFECTIVENESS — The cost-effectiveness of TOLAC depends upon the likelihood of VBAC. In a decision analytic model with a hypothetical cohort of 100,000 patients undergoing TOLAC versus PRCB, TOLAC was cost-effective when the probability of VBAC was >47.2 percent [94]. Although this model was based upon costs in 2009, the findings are likely to continue to be valid.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Cesarean birth".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Vaginal birth after a cesarean (The Basics)")

PATIENT PERSPECTIVE TOPIC — Patient perspectives are provided for selected disorders to help clinicians better understand the patient experience and patient concerns. These narratives may offer insights into patient values and preferences not included in other UpToDate topics. (See "Patient perspective: Trial of labor after cesarean birth".)

SUMMARY AND RECOMMENDATIONS

●Overview – Patients who have undergone a previous cesarean birth have the option of proceeding with a trial of labor after cesarean (TOLAC) or planned repeat cesarean birth (PRCB) in a subsequent pregnancy. Planned TOLAC may result in labor with vaginal birth (VBAC) or unplanned intrapartum cesarean birth. Decision-making regarding mode of birth must take into consideration the patient's personal preferences, obstetric history, the best available data on risks and benefits of TOLAC versus PRCB, and availability of TOLAC in the selected birth setting. (Related Pathway(s): Trial of labor after cesarean: Shared decision-making with a pregnant patient during the first prenatal visit.)

●Advantages of VBAC versus PRCB – The medical and obstetric benefits of successful VBAC derive from avoidance of the potential adverse outcomes associated with cesarean birth, especially multiple cesarean births. Conversely, the medical and obstetric benefits of PRCB derive from avoidance of the potential adverse outcomes associated with TOLAC, primarily uterine rupture and morbidity associated with intrapartum cesarean birth. (See 'Risks/benefits of TOLAC versus PRCB' above.)

●Person-centered decision-making – The decision for a TOLAC or PRCB is a person-centered decision made by the patient in collaboration with their provider. This decision involves a combination of factors, including (see 'Factors to consider in patient-centered decision-making' above):

•Availability of TOLAC at the planned birth setting. (See 'Facility resources for offering TOLAC' above.)

•Significance and estimated frequency of complications with TOLAC and PRCB, including individual patient factors that affect the risks and benefits for each birth route. The following table summarizes maternal outcomes associated with VBAC and PRCB (table 1); it was derived from a 2010 systematic review of 41 studies and is subject to several limitations. The maternal morbidity of TOLAC appears to be higher than that for PRCB when the predicted chance of vaginal birth is <60 to 70 percent. (See 'Risks/benefits of TOLAC versus PRCB' above.)

•Personal values, preferences, past birthing experiences, and future pregnancy plans.

•Probability of VBAC. (See 'Predicting the probability of VBAC' above.)

A patient who has undergone only one previous cesarean birth via a low transverse hysterotomy incision has the lowest risk of uterine scar separation during a subsequent trial of labor; thus, TOLAC is a reasonably safe option for these patients. The body of evidence suggests a VBAC rate of 60 to 80 percent, with an estimated uterine rupture rate of 0.4 to 0.7 percent. (See 'One prior low transverse uterine incision' above.)

In the author's practice, patients with a previous cesarean birth and a history of vaginal birth (either prior vaginal birth or VBAC) are encouraged to undertake a TOLAC, given that the VBAC rate has been reported to be as high as 83 percent for patients with a previous vaginal birth and 94 percent for patients with a previous VBAC. For patients outside of this small subset of the population, the author frequently uses a VBAC calculator (calculator 1) to inform them of their individual chance of achieving a vaginal birth. (See 'Our approach' above and 'VBAC calculators' above.)

●Inappropriate candidates for TOLAC – In patients with standard contraindications to labor or vaginal birth (eg, placenta previa), PRCB is required. In patients with a prior transfundal uterine incision or prior uterine rupture, we agree with the American College of Obstetricians and Gynecologists that the high risk of intrapartum uterine rupture during TOLAC favors PRCB. (See 'Inappropriate candidates' above.)

ACKNOWLEDGMENTS — The editorial staff at UpToDate acknowledge C Edward Wells, MD, and F Gary Cunningham, MD, who contributed to an earlier version of this topic review.