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INTRODUCTION — For women who have undergone a previous cesarean delivery, optimum management of subsequent deliveries has been debated for over 100 years [1-5]. The two options are trial of labor after cesarean delivery (TOLAC) and planned repeat cesarean delivery (PRCD).
This topic will review issues related to choosing the route of delivery after cesarean birth as well as management of a trial of labor in this setting. Uterine rupture is an infrequent but serious complication in women who attempt TOLAC and is discussed in detail separately. (See "Uterine rupture after previous cesarean delivery".)
BACKGROUND — In 1980, a National Institutes of Health Consensus Development Conference report questioned the necessity of routine PRCD and, with endorsement from the American College of Obstetricians and Gynecologists (ACOG) [6-8], encouraged clinicians and patients to increase the rate of TOLAC, with great success: The TOLAC rate reached a peak of 51.8 percent in 1995, with a concomitant decline in total cesarean delivery rates in the United States .
As the TOLAC rate increased, however, so did reports of uterine rupture-related maternal and perinatal morbidity [10-14]. These adverse outcomes dampened enthusiasm for TOLAC. They also prompted ACOG to issue a practice bulletin in 1998 that cautioned TOLAC should only be attempted in appropriately equipped institutions with clinicians "readily" available to provide emergency care . Within nine months, ACOG revised the practice bulletin to say that clinicians should be "immediately" available , a position endorsed by the American Society of Anesthesiologists [17,18]. After this change, national TOLAC rates declined, reaching a nadir of 15.9 percent in 2006 before increasing again . Two surveys of hospital administrators found that 30 percent of hospitals discontinued allowing TOLAC because they were unable to comply with the immediately available requirement for surgical and anesthesia services, and of the hospitals who continued to offer TOLAC, over half made changes in their policies to accommodate ACOG recommendations [19-21].
Fear of catastrophic complications associated with TOLAC may be one reason providers avoid encouraging TOLAC for their patients [19,22]. Concerns about medical liability claims have also contributed to reduced access to TOLAC [23-25]. For example, a 2009 Survey of Professional Liability by ACOG found that 91 percent of members who responded reported at least one liability claim against them in their career; 62 percent of claims within the survey period were related to obstetric care . Of those who made changes in their obstetric practice as a result of risk or fear of liability, 25 percent stopped offering TOLAC.
In spite of these concerns, it is important to remember that a successful uncomplicated TOLAC resulting in a vaginal birth after cesarean delivery (VBAC) has many short- and long-term benefits (see 'Risks and benefits of TOLAC versus PRCD' below). In a Markov model, when the likelihood of success was ≥47 percent, TOLAC was more effective and less expensive than PRCD . The cost-effectiveness improves in patients who undergo multiple subsequent vaginal deliveries .
LIMITATIONS OF AVAILABLE EVIDENCE — No large randomized trials have been performed to provide comparative data on outcomes of TOLAC versus PRCD; a systematic review identified only two randomized trials involving 320 women with minimal data for maternal and infant clinical outcomes .
It is important to recognize that many case-control and cohort studies that compared these two routes of delivery reported maternal and neonatal outcomes based on the actual route of delivery rather than the intended route. If this type of analysis is performed, the outcomes of women who undergo cesarean delivery after an unsuccessful TOLAC are grouped along with the outcomes of women undergoing PRCD, which is a less morbid procedure. In addition, the outcomes of women who planned PRCD but spontaneously labored and were delivered vaginally are grouped along with the outcomes of women who had a successful TOLAC. This method of analysis leads to misleading conclusions about the actual risk of adverse events or outcomes associated with the decision to attempt TOLAC or PRCD. Analysis of available 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 delivery.
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 study these issues . Their final report summarized the state of knowledge concerning the risks and benefits of PRCD versus TOLAC in women who have undergone one or more prior cesarean deliveries. These findings and subsequent data are described throughout this topic.
RISKS AND BENEFITS OF TOLAC VERSUS PRCD
Overview — There are two possible intended management options (intended TOLAC versus intended PRCD) that can lead to three possible outcomes for the woman who has had a prior cesarean delivery: a PRCD, a successful trial of labor culminating in vaginal birth, or a failed TOLAC resulting in a repeat cesarean delivery during labor. The medical and obstetric benefits of successful TOLAC derive from avoidance of the risks associated with repeat cesarean delivery, especially multiple cesarean deliveries: Most maternal morbidity associated with TOLAC occurs when intrapartum cesarean delivery becomes necessary. Conversely, the medical and obstetrical benefits of PRCD derive from avoidance of the risks associated with TOLAC, primarily uterine rupture. Thus, the benefits of TOLAC are closely related to having a successful vaginal birth, which has the lowest morbidity of the three possibilities. A failed TOLAC has higher morbidity than successful TOLAC or PRCD, especially if failed TOLAC is associated with uterine rupture, which can be fatal for the mother or child .
Maternal — The following table summarizes available evidence of maternal risks associated with TOLAC and PRCD (table 1); it was derived from a 2010 systematic review of 41 studies . A limitation of these data is that the studies reported outcomes based on the actual route of delivery rather than the intended route. This is important because maternal morbidity is higher when cesarean delivery is performed during labor. Selected risks of TOLAC are discussed 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 potentially life-threatening. The National Institute of Child Health and Human Development consensus conference panel described uterine rupture risk in the following way , based on data in the 2010 systematic review :
•In a hypothetical group of 100,000 women of any gestational age who undergo TOLAC, there will be 468 cases of uterine rupture. Looked at in another way, these data suggest that approximately 1 in 200 TOLACs will lead to uterine rupture.
•In a hypothetical group of 100,000 women of any gestational age who undergo PRCD, there will be 26 uterine ruptures.
The types and frequencies of major maternal and neonatal outcomes of uterine rupture include:
•Hysterectomy: 14 to 33 percent .
•Maternal death: 0.21 percent (4 deaths out of 1879 cases of uterine rupture without pre-existing conditions) .
•Neonatal death: 5 percent, adjusted odds ratio 65 .
•Severe neonatal neurologic morbidity: 6 to 8 percent [32,33].
●Infection – Although the overall risk of infection appears to be similar for TOLAC and PRCD , specific risks vary by clinical setting. For example, only women in labor are at risk for intrapartum chorioamnionitis. Successful TOLAC has a lower frequency of postpartum infection than PRCD, while intrapartum cesarean delivery has the highest frequency of postpartum infection .
●Peripartum hysterectomy – Although some peripartum hysterectomies are performed because of uterine rupture during TOLAC, many others are performed because of placenta accreta. An increasing number of cesarean deliveries increases the risk for placenta previa and, in turn, placenta accreta. (See "Clinical features and diagnosis of the morbidly adherent placenta (placenta accreta, increta, and percreta)", section on 'Risk factors'.)
●Other – PRCD avoids the potential risks and sequelae of pelvic trauma related to labor and vaginal birth; however, the magnitude of this effect compared with TOLAC is unclear and does not appear to outweigh the risks of PRCD. Pregnancy itself is the major risk factor for future pelvic relaxation disorders. (See "Urinary incontinence and pelvic organ prolapse associated with pregnancy and childbirth".)
For many patients, a benefit of PRCD is that scheduled delivery allows her and her family the ability to make specific work-life plans for the delivery and postpartum period. Although induction of labor can also be scheduled, TOLAC is safer when labor is spontaneous and thus somewhat unpredictable. Personal benefits of successful TOLAC include shorter hospital stay and quicker return to normal activities compared with PRCD.
Postpartum sterilization is readily accomplished at cesarean delivery; however, this is a minor advantage of PRCD since sterilization can be performed after a vaginal birth and often immediately following the birth.
Neonatal — Evidence for short- and long-term neonatal outcomes after TOLAC versus PRCD is limited . As discussed above, most of the available evidence documents differences comparing actual rather than intended mode of delivery and is of low quality due to inconsistent and imprecise outcome measures. The 2010 systematic review discussed above reported the following neonatal outcomes relating to TOLAC :
●Perinatal mortality and neonatal mortality rates were higher with TOLAC than for PRCD (perinatal mortality rate: 0.13 versus 0.05 percent; neonatal mortality rate: 0.11 versus 0.06), although the absolute risk is very low.
●Transient tachypnea of the newborn was more common with PRCD compared with TOLAC (4.2 versus 3.6 percent). However, neonatal bag and mask ventilation was used more often in infants delivered following TOLAC than in those delivered by PRCD (5.4 versus 2.5 percent).
●Data were insufficient to determine the direction of risk for hypoxic ischemic encephalopathy, sepsis, trauma, neonatal intensive care unit (NICU) admission, and neurologic outcomes.
Subsequent studies have observed that the rates of suspected and proven neonatal sepsis are higher for TOLAC than PRCD (suspected sepsis 5 versus 2 percent; proven sepsis 1 versus 0 percent)  and observed an increased risk of neonatal depression and NICU admission with TOLAC versus PRCD [36,37].
SHARED DECISION-MAKING — Planning the route of delivery for the woman who has had a previous cesarean delivery should be addressed early in her prenatal care and can begin preconceptionally. The decision for TOLAC or PRCD should be a collaborative process between patients and their providers that takes into account the best clinical evidence available as well as the patient's values and preferences. Whenever possible, the woman's preference should be honored [19,22]. Ongoing discussion at intervals throughout pregnancy is important, as conditions may arise that alter the balance of risks and benefits of the planned route of delivery.
Individual patient factors that impact the risks and benefits for each delivery method should be discussed. This is especially important for women who are potentially at higher risk of uterine rupture and its attendant sequelae and women who may have more than two cesarean deliveries. (See 'Candidates for TOLAC' below.)
Factors known to affect TOLAC success rates and the patient's likelihood of success obviously need to be addressed. Between 1990 and 2009, the success rate for women in the United States who attempted TOLAC ranged from 39 to 70 percent . The success rate varies among institutions and providers and is affected by antepartum, intrapartum, and nonmedical factors . (See 'Candidates for TOLAC' below.)
A woman's decision regarding route of delivery is also influenced by other factors. Common reasons women choose TOLAC include a prior successful vaginal delivery since it is associated with an increased chance of successful TOLAC and decreased risk of uterine rupture, future pregnancy plans since multiple cesarean deliveries increase the risk for placenta previa/accreta, family obligations making a speedy return to normal activities postpartum desirable, the desire to experience a natural birth, and desire for their partners' involvement in labor and birth. Common reasons women choose PRCD include scheduling convenience, ease of sterilization at the time of delivery, fear of failed trial of labor and emergency cesarean delivery, and avoidance of labor pain [19,22]. In addition, women report that their health care providers' recommendations and preferences exert a strong influence on their decision whether or not to pursue TOLAC .
Unlike most medical decisions where patients are comparing risks and benefits for themselves, the pregnant patient must compare risks and benefits for both herself and her fetus, and the risks and benefits for these two individuals sometimes do not align: A decision that increases maternal risk may be associated with fetal benefit. It should be noted that most pregnant women are willing to tolerate a high degree of risk to themselves in exchange for zero or near-zero risk for their child [39,40]. Though, occasionally, the desire to achieve a natural birth can lead to increasing the risk to their child as in the case of the out-of-hospital TOLAC [41-44].
Decision aids — A number of patient-oriented information and decision aids (table 2) are available to help patients make an informed decision about TOLAC versus PRCD. In the United States, patient information is available from the American College of Obstetricians and Gynecologists and from the National Library of Medicine.
Online tools or decision aides can be used as an adjunct to provider consultation. They are designed to communicate evidence-based information to help patients better understand childbirth choices, establish their personal priorities, and ultimately decide whether or not to pursue a TOLAC.
A prospective study found that many patients with a prior cesarean are insufficiently informed of the complexities of the issues when they make their decision on route of delivery . Although a Cochrane review found that the use of decision support tools used independently by the patient ultimately made no difference in the type of birth (TOLAC versus PRCD) women planned, the use of these tools reduced feelings of uncertainty about their decision .
CANDIDATES FOR TOLAC
Overview — The ideal candidates for TOLAC are women with a high likelihood of vaginal delivery and a very low likelihood of intrapartum uterine rupture. The paucity of definitive data predictive of these outcomes makes selecting ideal candidates challenging.
The authors do not use calculators or other tools to predict TOLAC outcome. A number of predictive models, screening tools, and nomograms have been developed to identify women with a prior cesarean delivery who have a high or low likelihood of successful TOLAC, but none have been proven to be highly useful clinically [19,22,46-49]. These screening tools use a combination of obstetric factors, such as maternal demographics (age, race, ethnicity, body mass index [BMI]); the indication(s) for the prior cesarean delivery; the type and number of prior hysterotomy incisions; previous vaginal deliveries, either before or after the cesarean delivery; cervical favorability (eg, Bishop score at the time of admission for spontaneous or planned induction of labor); and intrapartum interventions (eg, labor induction or augmentation) . One review concluded that scored screening tool models incorporating various combinations of the above predictive factors reasonably predicted successful TOLAC but were unable to consistently identify women at risk for failed TOLAC . The use of calculators as part of the process of counseling women about TOLAC is reviewed in detail separately. (See "Use of calculators and models for predicting vaginal birth after a previous cesarean delivery".)
There is also no reliable method for predicting uterine rupture in women with a prior cesarean delivery. Likelihood of rupture is estimated primarily by type of hysterotomy incision and presence/absence of risk factors; some clinicians also perform sonographic evaluation of the hysterotomy scar. Methods for prediction of uterine rupture and their performance are reviewed separately. (See "Uterine rupture after previous cesarean delivery", section on 'Predicting uterine rupture'.)
One prior low transverse uterine incision — There is good and consistent evidence that a woman who has undergone only one previous cesarean delivery performed using a transverse lower segment hysterotomy incision has the lowest risk of uterine scar separation during a subsequent trial of labor; thus, TOLAC is a reasonably safe option for delivery for these women [19,22]. In this setting, the body of evidence suggests a TOLAC success rate of 60 to 80 percent , with an estimated uterine rupture rate of 0.4  to 0.7 percent . Success rates are higher in patients with additional characteristics, such as a prior vaginal delivery.
Characteristics that increase the probability of successful TOLAC in this population — For women who are optimal candidates for TOLAC, the highest success rates (over 80 percent) occur in those with:
●A successful vaginal delivery before or after their primary cesarean delivery – These women are significantly more likely to have a successful TOLAC than those who have never delivered vaginally (odds ratio [OR] for successful TOLAC with prior vaginal delivery 3.90, 95% CI 3.60-4.30; with prior successful TOLAC 4.76, 95% CI 4.35-5.26) . In addition, one study reported that women with a previous vaginal delivery had one-fifth the risk of uterine rupture during TOLAC compared with women without prior vaginal delivery (0.2 versus 1.1 percent) .
●A nonrecurrent indication for their primary cesarean delivery – The rate of successful TOLAC by indication for prior cesarean delivery is approximately 75 percent for fetal malpresentation, 60 percent for nonreassuring fetal heart rate pattern, and 54 percent for failure to progress or cephalopelvic disproportion [22,53].
●Spontaneous labor on admission to the labor unit – When admitted to the labor unit, women in spontaneous labor or with >4 cm cervical dilation are more likely to have successful TOLAC than women without these characteristics (OR for successful TOLAC with spontaneous labor, induction, augmentation 1.0, 0.50, 0.68, respectively; for admission cervical examination >4 cm 2.56, 95% CI 2.38-2.67) [22,53].
Additional characteristics that increase the probability of successful TOLAC are discussed below.
●Fetal weight less than 4000 g – An estimated fetal weight >4000 g halves the likelihood of successful TOLAC (successful TOLAC for birth weight >4000 g OR 0.55, 95% CI 0.49-0.61) [22,53,55,56].
●Demographic factors – Hispanic, African American, and Asian women are more likely to pursue a TOLAC but are less likely to have a successful TOLAC when compared with non-Hispanic white women (OR for successful TOLAC for non-Hispanic Caucasians, African Americans, and Hispanics: 1, 0.69, and 0.65, respectively) [22,46,53,57-59].
Women over 35 years of age are less likely to pursue a TOLAC; those who attempt TOLAC are less likely to have a successful TOLAC and more likely to experience TOLAC-associated complications than younger women .
The likelihood of successful TOLAC increases with increasing maternal height (for each 5 cm maternal height increase the OR for successful TOLAC is 1.33, 95% CI 1.28-1.37) and is lower in obese women (for BMI >30 kg/m2, the OR for successful TOLAC is 0.55, 95% CI 0.51-0.60) [46,53,61].
●Interpregnancy interval more than six months – An interpregnancy interval of more than six months is desirable, as an interval of less than six months is an independent risk factor for both uterine rupture and maternal morbidity during TOLAC. (See "Interpregnancy interval and obstetrical complications".)
●Absence of maternal medical disease – Data on the effect of pre-existing maternal medical disease on the outcome of a TOLAC are inconclusive. Several cohort studies of women with pre-existing maternal disease, such as hypertension, diabetes, asthma, renal disease, and heart disease, reported a reduced likelihood of successful TOLAC [53,58,62]. In one prospective study, however, there were no significant differences in the rates of successful TOLAC in women with these medical disorders .
●Delivery in a university hospital – University hospitals or hospitals affiliated with an obstetrics and gynecology residency program have higher rates of TOLAC and successful TOLAC [56,63,64]. Women who deliver at a private or rural hospital have a decreased likelihood that TOLAC will be attempted and, if attempted, a decreased rate of successful TOLAC when compared with a tertiary care or perinatal center . As an example, a study that compared successful TOLAC rates across hospital settings in California reported rates of successful TOLAC (adjusted for baseline and medical characteristics of mother and fetus) as 14 percent in private nonteaching hospitals, 57 percent in public hospitals, 60 percent in private teaching hospitals, and 41 percent in health maintenance organizations .
Possibly appropriate candidates — Women who are possibly appropriate candidates for TOLAC have a reasonable likelihood of success but lower than in optimal candidates. They also have a low likelihood of uterine rupture, but data regarding their risk of uterine rupture are more limited than in optimal candidates and based on sparse or inconsistent scientific evidence.
The American College of Obstetricians and Gynecologists (ACOG) has opined that women with the following clinical characteristics can be considered candidates for TOLAC, after appropriate individualized risk assessment and counseling (table 3) :
Prior low vertical uterine incision — Data are limited and inconclusive regarding risk of uterine rupture in women with a prior low vertical uterine incision. A literature review concluded the frequency of rupture for low transverse uterine incisions ranged from 0.4 to 0.7 percent versus 1.05 to 2.0 percent for low vertical uterine incisions .
Two prior low transverse uterine incisions — The likelihood of successful TOLAC appears to be similar for women with one versus two prior cesarean deliveries (65 to 75 percent) [68-70]; however, women with more than one prior cesarean appear to have a higher rate of uterine rupture In a 2010 systematic review with meta-analysis of five cohort studies of uterine rupture in women with prior cesarean deliveries, women undergoing TOLAC after one prior cesarean were at significantly lower risk of rupture than those with two prior cesareans (0.72 versus 1.59 percent; OR 0.42, 95% CI 0.29-0.60); however, the definition of rupture varied among studies .
Unknown type of uterine incision — The prior incision type is not always available when caring for a woman in her subsequent pregnancy. Because most women with a prior uterine incision for common obstetrical indications have had a low-transverse hysterotomy incision, some authors suggest making the decision for TOLAC based on this assumption. This approach is supported by data from two large studies that found women 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 [34,71]. As an example, uterine rupture occurred in 0.5 percent of women with an unknown scar type and 0.7 percent of women 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 .
There are a few indications for cesarean delivery that increase the probability of a prior vertical incision, such as breech delivery remote from term or transverse lie; thus, the circumstances of the prior cesarean delivery should be considered in estimating whether the patient is at increased risk of uterine rupture when the operative report is unavailable.
Pregnancy more than 40 weeks of gestation — Studies have consistently observed that women who attempt TOLAC beyond 40 weeks of gestation are less likely to successfully deliver vaginally [19,55,72]. In addition, there are at least two reports that have described a 2 to 3 percent risk of uterine rupture in these women [73,74].
The authors discuss both of these issues with patients who are planning TOLAC and offer induction of labor by amniotomy at 40 weeks of gestation if the cervix is favorable. If the cervix is unfavorable, mechanical cervical ripening followed by amniotomy and oxytocin administration is an option. (See "Cervical ripening and induction of labor in women with a prior cesarean delivery".)
Twin gestation — While most studies report that women 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 [75-77]. ACOG has opined that women with twin pregnancies and one previous low transverse cesarean delivery are candidates for TOLAC if they have no contraindications to vaginal birth . (See "Twin pregnancy: Labor and delivery", section on 'Trial of labor after previous cesarean delivery'.)
Macrosomia — When counseling women regarding TOLAC, ACOG has opined that suspected fetal macrosomia (EFW ≥4000 grams) alone should not preclude the option of a TOLAC . Clinicians should consider whether the woman has had a previous vaginal delivery, past birth weight(s) and outcomes, and the predicted birth weight in the current pregnancy. However, prophylactic cesarean delivery has been suggested when the estimated fetal weight is ≥5000 grams in women without diabetes and ≥4500 grams in women with diabetes .
For women with no previous vaginal delivery, the likelihood of successful TOLAC falls to ≤50 percent when birth weight increases above 4000 grams [80,81]. In one study of TOLAC among such women, newborn birth weights <4000 grams, 4000 to 4249 grams, 4250 to 4500 grams, and >4500 grams were associated with vaginal birth after cesarean in 68, 52, 45, and 38 percent of cases, respectively . Success rates were lower if the indication for the previous cesarean delivery was cephalopelvic disproportion or failure to progress or if the woman required either induction or augmentation of labor during TOLAC. In contrast, women who had a previous vaginal delivery had a ≥63 percent rate of vaginal birth after cesarean for any of the birth weight strata.
It also should be noted that women attempting TOLAC with no prior vaginal delivery and/or newborn birth weight >4000 grams may have a higher likelihood of adverse obstetrical outcomes, such as uterine rupture [80,82,83]. In one study, women attempting TOLAC with both no prior vaginal delivery and newborn birth weight ≥4000 grams had a 3.6 percent uterine rupture rate .
Maternal diabetes — Rates of successful TOLAC in women with gestational and pregestational diabetes appear to be lower compared with nondiabetic women undergoing TOLAC [84-86]. The authors do not offer TOLAC to women whose pregnancies are complicated by gestational or pregestational diabetes, but our approach is not universal.
Maternal obesity — Observational studies have consistently reported that a trial of labor after a cesarean delivery is less likely to result in vaginal birth in obese gravidas [22,46,53,86-91]. The largest of these studies was a prospective multicenter study including 6413 obese and 1638 severely obese women . The rate of failed trial of labor was 15 percent in normal-weight women, 30 percent in obese women, and 39 percent in severely obese women. 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 severely obese women or at any threshold BMI. ACOG has opined that women who have a BMI of ≥30 may be candidates for TOLAC and characteristics, such as a prior vaginal delivery, should be considered in case-by-case decision making . The authors do not have a specific limitation related to BMI.
Inappropriate candidates — Most clinicians, including these authors, believe the risks of TOLAC outweigh the benefits in the following settings:
High-risk uterine scars
Prior classical, T, or J hysterotomy — Types of prior hysterotomy incisions that have an unacceptably high risk for uterine rupture during TOLAC include classical, T, or J incisions as well as transfundal incisions or myoma resections that extend into the myometrium. In the literature review discussed above, the frequency of rupture for classical or T-shaped incisions ranged from 4.0 to 9.0 percent, which is at least two-fold higher than the upper estimate of rupture risk for low vertical incisions and more than five-fold higher than the upper estimate of rupture risk for low transverse uterine incisions .
A NICHD MFMU Network study of TOLAC evaluated the outcome of women with prior classical or either inverted T or J incision who presented in advanced labor or declined repeat cesarean delivery . The uterine rupture rate was lower than expected in this study, 1.9 percent, but still unacceptably high in the authors' opinion. A subsequent retrospective study of women attempting TOLAC found that a prior inadvertent uterine extension at the time of primary cesarean was associated with an increased risk of uterine rupture when compared with no prior extension (6.0 versus 1.5 percent) .
Thin lower uterine segment thickness — Sonographic lower uterine segment thickness near term is inversely correlated with the risk of uterine scar dehiscence or rupture at delivery. However, use of imaging techniques to predict women at increased risk of uterine rupture during TOLAC has had mixed results. Despite its limitations, many authors consider a full lower uterine segment thickness <2.0 mm predictive of an increased risk of rupture or dehiscence. These data are reviewed separately. (See "Uterine rupture after previous cesarean delivery", section on 'Use of imaging'.)
Prior uterine rupture — Women 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 [93-97]. Women in whom the prior rupture involved the upper uterine segment have experienced a repeat rupture rate as high as 32 percent . In a 25-year literature review, 22 women identified to have uterine rupture subsequently became pregnant again . Twenty underwent PRCD at term; the other two women died following catastrophic uterine rupture at 32 and 35 weeks of gestation. Although the overall quality of this evidence is low, the risk of rupture in these patients is likely unacceptably high. (See "Repeat cesarean delivery", section on 'Previous classical incision'.)
Women with prior uterine rupture, prior classical cesarean delivery, or prior hysterotomy for fetal surgery  are all at increased risk of scar dehiscence or rupture in subsequent pregnancy and thus should undergo delivery by PRCD by 37 weeks of gestation. Management of these pregnancies are reviewed separately. (See "Uterine rupture after previous cesarean delivery", section on 'Management of subsequent pregnancies'.)
Prior uterine dehiscence — For women who have experienced a prior uterine scar dehiscence and repair, the likelihood of subsequent uterine rupture with potential catastrophic outcome is unclear. There have been isolated reports of both antepartum and interpregnancy uterine scar repairs followed by successful pregnancies; however, numbers are small and await confirmation on a larger scale. While consensus recommendations for the management of these women are not available, the authors do not offer TOLAC and plan delivery by PRCD at 37 weeks of gestation [99,100]. (See "Uterine rupture after previous cesarean delivery", section on 'Recurrence risk'.)
Contraindication to vaginal delivery — PRCD should be performed when standard obstetrical contraindications to vaginal delivery are present, such as placenta previa or footling breech presentation.
Fetal demise — The balance of risks and benefits is different in the setting of fetal demise since PRCD has no perinatal benefit. Decision-making on the route of delivery in these cases is reviewed separately. (See "Fetal death and stillbirth: Maternal care".)
MANAGEMENT OF LABOR AND DELIVERY — Intrapartum management of patients undergoing TOLAC is similar to that in patients with an unscarred uterus, except they are more closely monitored for signs of uterine rupture, especially when uterotonic agents are administered.
Facilities and personnel — The ability to perform emergency cesarean delivery is a prerequisite for attempting TOLAC in women with any type of prior hysterotomy incision. The American College of Obstetricians and Gynecologists (ACOG) recommends that TOLAC be undertaken in facilities with immediate availability of appropriate resources, including equipment and personnel (obstetric anesthesia, nursing personnel, a clinician capable of monitoring labor and performing an emergency cesarean delivery, personnel and equipment for neonatal resuscitation) .
In situations in which such resources are not immediately available, ACOG recommends a discussion between the provider and patient to discuss implications of the lack of immediately available personnel. One antepartum option is referral to another facility with appropriate resources to obtain optimal outcomes. However, some doctors and patients may elect to proceed with TOLAC even if all desirable conditions cannot be met. In all cases, any decision to plan for TOLAC in a setting lacking immediately available resources should be made only after careful consideration by the woman and her health care provider. In such instances, the discussion and plan should be documented in the obstetrical record.
Intrapartum monitoring — Given an increased risk of uterine rupture, most experts recommend continuous monitoring of uterine activity and fetal heart rate during TOLAC; there are no data to show superiority of external versus internal monitoring methods . Intrauterine pressure monitoring is unnecessary, as it is an insensitive method for early diagnosis of uterine rupture [101,102].
Labor pattern — Labor progress between 4 and 7 cm in women with no previous vaginal births appears to be slightly longer than that in nulliparous women in spontaneous labor . Labor patterns in women who have delivered vaginally are similar to those in multigravidas .
Induction and augmentation of labor — Some women who plan TOLAC will develop a maternal or fetal indication for delivery before the onset of spontaneous labor. The benefits and harms of PRCD versus induction of labor have not been evaluated by randomized trials . While there is no conclusive evidence that uterotonic drugs administered to women with a prior cesarean delivery increase the risk of uterine rupture, epidemiological studies suggest that this is the case [34,106-108]. For this reason, we suggest a cautious approach to labor induction or augmentation in women planning/undergoing TOLAC, especially those with an unknown type of uterine scar, unfavorable cervix, or gestational age over 40 weeks [55,109,110]. ACOG considers both induction and augmentation reasonable options for TOLAC patients, when indicated .
●Induction – If the cervix is dilated and favorable, our preference is to perform amniotomy to induce labor in women with one previous cesarean delivery. A professional consensus opined against induction in women with two previous cesareans .
In a practice bulletin, ACOG recognized induction of labor with oxytocin or a mechanical method such as a bladder catheter balloon as options for women undergoing TOLAC . We agree with ACOG and others that misoprostol (prostaglandin E1) should not be used for cervical ripening or labor induction in the third trimester in women with prior uterine incisions and we strongly discourage use of other prostaglandins (PGE2) as well [111-114].
Two concerns about inducing labor in women with a prior cesarean delivery are an increased risk for uterine rupture and a lower probability of successful TOLAC [115,116], according to data from observational studies. A prior vaginal delivery or favorable cervix (eg, Bishop score of >6) increases the probability of successful TOLAC with labor induction. Induction with oxytocin or mechanical methods appears to have a lower risk for uterine rupture than prostaglandins. These issues and supporting evidence are discussed in detail separately. (See "Cervical ripening and induction of labor in women with a prior cesarean delivery", section on 'Risk of rupture'.)
●Oxytocin augmentation – Women whose labors do not follow generally accepted standards of labor progress in the active phase are managed with oxytocin augmentation or repeat cesarean delivery, as appropriate. Despite a paucity of high-quality data, given the relative infrequency with which uterine rupture occurs, ACOG supports use of oxytocin for augmentation of labor in women with a previous cesarean delivery .
There are conflicting data on the risk of uterine rupture from oxytocin augmentation of labor during TOLAC. Three large observational studies reported an increased risk for uterine rupture with labor augmentation (odds ratio [OR] 2.3 to 14, actual rate of rupture 0.9 to 1.9 percent) [34,117,118], and two others did not find an increased risk [119,120]. Small numbers of uterine ruptures and use of prostaglandin analogues for cervical ripening prior to augmentation of labor prevent definitive conclusions based on these results.
It is unclear whether oxytocin regimens should be modified or an upper dose limit should be set in women undergoing TOLAC; this issue has not been evaluated extensively. A case-control study reported an increasing risk of uterine rupture with increasing oxytocin dose; the authors suggested an upper limit of 20 milliunits/min . Another study found the risk of rupture was primarily related to hyperstimulation . The low incidence of uterine rupture limits the power of these studies to detect small differences in dose-related risk of rupture.
Although clinicians generally have a lower threshold for diagnosing failure to progress in women undergoing TOLAC than in women with an unscarred uterus, evidence-based guidance does not exist. Based on expert consensus, the French College of Gynecologists and Obstetricians suggests that the total duration of failure to progress before performing cesarean delivery in the active phase should not exceed three hours for women with a previous cesarean .
Analgesia and anesthesia — Epidural analgesia may be used to provide adequate pain relief during labor . Epidural analgesia does not appear to mask the signs and symptoms of uterine rupture and/or reduce the chance of successful TOLAC . However, a prospective cohort study reported an increased risk of rupture in patients who had epidural anesthesia (OR 2.2, 95% CI 1.1-4.9) .
Amnioinfusion for management of variable decelerations — In women with an unscarred uterus and variable decelerations during labor, a systematic review of observational studies found that amnioinfusion was associated with a reduction in cesarean delivery and improvement in some neonatal outcomes . The risks of rare, but serious, adverse effects were not measurable.
There are even fewer data on amnioinfusion in women undergoing TOLAC [52,123-125]. Uterine ruptures have been reported in these patients [52,124,125], but it is unknown whether the rates of rupture and cesarean delivery are different from the rates in women undergoing TOLAC with variable decelerations not treated with amnioinfusion. Given the paucity of safety and efficacy data, the authors do not manage variable decelerations with amnioinfusion in women undergoing TOLAC.
Clinical findings, diagnosis, and management of uterine rupture — (See "Uterine rupture after previous cesarean delivery".)
Uterine exploration at delivery — Some clinicians recommend routine uterine exploration following uncomplicated successful TOLAC, while others only perform exploration for standard obstetrical indications, such as retained placenta or hemorrhage . There are no data on the value of routine examination to identify asymptomatic uterine dehiscence or whether repair is indicated, but the authors routinely perform uterine exploration following uncomplicated successful TOLAC. Identification of an asymptomatic uterine defect following vaginal delivery does not warrant immediate therapy. These patients are referred to the gynecology service postpartum for evaluation and possible treatment of isthmocele (ie, a pouch-like defect at the site of a previous cesarean delivery scar) .
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 delivery".)
SUMMARY AND RECOMMENDATIONS
●Pregnant women with a prior cesarean birth must choose between planned repeat cesarean delivery (PRCD) and a trial of labor after cesarean delivery (TOLAC). Obstetrical and personal factors impact this decision and should be discussed when counseling the patient (table 4). Her final decision will be based upon her individual clinical circumstances, tolerance for the various risks involved, personal values, and availability of a facility capable of emergency cesarean delivery if required. (See 'Shared decision-making' above.)
●Decision aids and calculators that predict probability of VBAC (vaginal birth after cesarean delivery) can help patients make a choice re: TOLAC versus repeat cesarean delivery. (See 'Decision aids' above and "Use of calculators and models for predicting vaginal birth after a previous cesarean delivery".)
●The medical and obstetric benefits of successful TOLAC derive from avoidance of the risks associated with repeat cesarean delivery, especially multiple cesarean deliveries: Most maternal morbidity associated with TOLAC occurs when intrapartum cesarean delivery becomes necessary. Conversely, the medical and obstetrical benefits of PRCD derive from avoidance of the risks associated with TOLAC, primarily uterine rupture. Thus, the benefits of TOLAC are closely related to having a successful vaginal birth, which has the lowest morbidity of the three possibilities. (See 'Overview' above.)
●The following table summarizes available evidence of maternal risks associated with TOLAC and PRCD (table 1). In a hypothetical group of 100,000 women at term who undergo TOLAC rather than PRCD, there will be 9 fewer maternal deaths, 650 additional uterine ruptures, and 50 additional neonatal deaths. Looked at in another way, these data suggest that approximately 1 in 200 TOLAC will lead to uterine rupture and approximately 1 in 750 TOLAC will result in perinatal death. (See 'Risks and benefits of TOLAC versus PRCD' above.)
●A woman with a singleton gestation who has undergone only one previous cesarean delivery performed using a transverse lower segment hysterotomy incision has the lowest risk of uterine scar separation during a subsequent trial of labor; thus, TOLAC is a reasonably safe option for delivery for these women. In this setting, TOLAC success rates are 60 to 80 percent, with an estimated uterine rupture rate of 0.4 to 0.7 percent. Success rates are higher in patients with additional characteristics, such as a previous successful TOLAC, previous vaginal delivery, previous cesarean delivery for nonvertex presentation, and in women with spontaneous onset of labor. (See 'Optimal candidates' above.)
●For women with a prior low vertical incision, more than one previous low transverse uterine incision, unknown incision type, twin gestation, or macrosomia, the likelihood of TOLAC success and/or the risk of uterine is less favorable than for optimal candidates. After thorough counseling, some women may choose to attempt TOLAC. (See 'Possibly appropriate candidates' above.)
●Women with a previous classical, T, or J hysterotomy incision; uterine rupture; or extensive transfundal surgery are at high risk of uterine rupture and should avoid TOLAC. The woman should have no contraindications to vaginal delivery and the facility should be able to perform an emergency cesarean delivery, if required. (See 'Inappropriate candidates' above and 'Facilities and personnel' above.)
●Women who attempt TOLAC beyond 40 weeks of gestation are less likely to successfully deliver vaginally and may be at higher risk of uterine rupture. The authors discuss both of these issues with patients who are planning TOLAC and offer induction of labor by amniotomy at 40 weeks of gestation if the cervix is favorable. (See 'Pregnancy more than 40 weeks of gestation' above.)
●Observational data suggest that uterotonic drugs administered for induction or augmentation of labor increase the risk of uterine rupture in women with a prior cesarean delivery. For this reason, we suggest a cautious approach to labor induction or augmentation in women undergoing TOLAC, especially those with an unknown type of uterine scar, unfavorable cervix, or gestational age over 40 weeks. We agree with the American College of Obstetricians and Gynecologists and others that misoprostol (prostaglandin E1) should not be used for cervical ripening or labor induction in the third trimester in women with prior uterine incisions and strongly discourage use of other prostaglandins as well. We use amniotomy and/or oxytocin to induce labor and mechanical methods for cervical ripening. (See 'Induction and augmentation of labor' above.)
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