Vaginal Birth after Cesarean and Trial of Labor after Cesarean: What should we be Recommending Relative to Maternal Risk: Benefit?

Abstract

Trial of labor after cesarean (TOLAC) delivery is currently a hot obstetrical topic owing to the acute rise in the rate of cesarean deliveries, both primary and repeat. When the physician and patient are considering TOLAC, several factors should be considered: risk of uterine rupture, contraindications, minimizing risk and morbidity, choosing the appropriate candidate and whether or not to induce. Each patient has her own set of individual risk factors that may decrease her chance of successful vaginal birth after cesarean delivery or increase her risks with TOLAC. Once all things are considered, the risk: benefit of TOLAC should be weighed up before a decision is reached. Each of these factors is discussed in respect to maternal risk: benefit, with the focus on evidence presented in the current literature.

Keywords

cesarean delivery contraindications induction of labor maternal morbidity trial of labor after cesarean delivery uterine rupture vaginal birth after cesarean delivery

In general, vaginal birth after cesarean (VBAC) delivery is considered a safe alternative to elective repeat cesarean delivery (ERCD), with between 60 and 80% of attempts at VBAC resulting in a successful vaginal birth [1,2]. Despite these statistics, enthusiasm for VBAC has waxed and waned depending on the changing recommendations in obstetric literature. The variation in published recommendations, along with changes in the medico–legal climate, has left obstetricians in a quandary over how to counsel potential candidates for VBAC and whether to offer a trial of labor after cesarean (TOLAC). As a result, cesarean delivery (CD) rates in the USA are currently at their highest, at approximately 32%, with almost a third of primary CDs occurring in nulliparas [3,4]. Although primary CD accounts for larger numbers of cesareans, ERCD is the most common indication for CD owing to the decline in VBACs in recent years [5]. This explains much of the observed increase in the rate of CDs.

Owing to the significant reduction in VBAC rates, a NIH consensus conference examined the safety and outcomes of TOLAC and VBAC as well as factors associated with the decreasing rate of VBACs [101]. Although the NIH panel agreed that TOLAC is a realistic choice for women with a previous CD and encouraged improving access to TOLAC, it acknowledged that the medico–legal climate impacts the decisions of institutions and their doctors to offer TOLAC. In response to this statement, the American Congress of Obstetricians and Gynecologists (ACOG) reviewed the risks and benefits of TOLAC and provided practical guidelines for managing and counseling patients undergoing TOLAC [6]. While current guidelines consider TOLAC and VBAC to be a valid alternative to ERCD, the CD rate remains high, primarily due to fear of uterine rupture, reluctance of physicians to offer TOLAC/VBAC, maternal and physician convenience, fear of litigation and concern for newborn well-being.

Notwithstanding the concerns of physicians, the restrictions in some healthcare facilities and the differing opinions of leading authorities on the topic it is essential that all parties involved in decision-making recognize that, for women with a history of a prior low transverse cesarean delivery (LTCD), the mode of delivery associated with the least maternal morbidity is successful VBAC [7]. However, the 2010 NIH Consensus Statement reported that when considering neonatal and fetal mortality, hypoxic–ischemic encephalopathy and brachial plexus palsy, ERCD was safest for the fetus [101]. The goal of the obstetric community should be to choose the mode of delivery that minimizes potential morbidity involving both the woman and fetus [7]. Even when facing the unknowns surrounding TOLAC and VBAC, we have a grasp on the signs of uterine rupture and the potential risks of a patient undergoing TOLAC. However, there is no definitive consensus on who are the best candidates for TOLAC and if induction is safe during TO LAC and, if so, what method of induction should be used. Each of these is discussed below with regards to maternal risk: benefit with recommendations based on the current literature.

Signs of uterine rupture

At the heart of the VBAC debate is the trepidation regarding uterine rupture. For obstetricians who have managed it, the indelible memory typically alters practice for a period of time if not indefinitely. Even though we can identify some patients at the greatest risk of uterine rupture and thus counsel against a TOLAC, most candidates for TOLAC do not have such clear-cut contraindications. As a result, the obstetrician must remain vigilant for any sign that may indicate a uterine rupture is impending or occurring. Currently, the only accessible tools to assist in making this diagnosis are electronic fetal monitoring and changes in patient complaints and/or status. For this reason, continuous electronic fetal monitoring and close monitoring for patient status changes are recommended during TOLAC. Both can be subjective, making the intuition of the obstetrician paramount in the diagnosis of uterine rupture and the decision to proceed to surgery.

Because the most common sign associated with uterine rupture is an abnormal fetal heart rate (FHR) tracing (up to 70% of cases), continuous FHR monitoring during labor is recommended [6,8 –10]. In a cohort study by Rageth and colleagues, nonreassuring FHR status was associated with uterine rupture (relative risk [RR]: 3.85; 95% CI: 2.67–5.55) [11]. Typically, a FHR tracing may herald signs of impending rupture prior to the actual rupture occurring. However, once rupture occurs, deep, repetitive and prolonged variable decelerations (classic pattern) and recurrent late decelerations may occur [12,13], followed by bradycardia [14] and then absent FHR. It is common practice to use internal monitoring on all patients attempting TOLAC and to explain to the patient that adequate FHR monitoring is essential, and if this cannot be accomplished, CD will be recommended. In addition, if suboptimal monitoring is making interpretation of the FHR difficult and there is a contraindication to internal monitoring, we will proceed with repeat CD.

Box 1.

Signs and symptoms of uterine rupture.

Maternal signs/symptoms

Tachycardia [13]

Hypotension [8,13]

Vaginal bleeding [6,12,13]

Gross hematuria [12]

Shock [12]

Loss of fetal station [6,13]

Uterine/abdominal pain [6,8,12,13]

Shoulder pain [12]

Anxiety/restlessness [12]

Weakness [12]

Dizziness [12]

Abnormal FHR tracings [6,8,12,13]

Prolonged, repetitive and/or deep variable decelerations

Recurrent late decelerations

Bradycardia

Absent FHR

Tocometry changes [6,12]

Decrease/change in frequency of contractions

Other signs and symptoms of acute uterine rupture are included in Box 1 [6,8,9,12,13]. If intra-abdominal bleeding occurs, the patient may experience more profound symptoms. Often the patient will experience one or more of these signs and symptoms just before and/or during the uterine rupture. For example, if a vaginal exam reveals loss of fetal station after a previous exam showed an engaged presenting fetal part, utering rupture should be suspected. If a patient has sudden onset of nausea and vomiting, especially during the second stage of labor, or if there is acute vaginal (or intra-abdominal) bleeding with a concomitant change in vital signs, uterine rupture is likely. A case–control study of 26 patients with uterine rupture found that mild and severe variable FHR decelerations, especially in the presence of persistent abdominal pain, associates strongly with uterine rupture in patients undergoing TOLAC [15]. At less than 2 h before delivery or acute uterine rupture, mild and severe variable decelerations, persistent abdominal pain and uterine hypersrimulation were more common [15].

During counseling of the patient for TOLAC, we explain that there may be a situation in which emergency CD is needed with a room full of personnel and procedures happening quickly. Alerting her to this possibility allows our measures to progress rapidly and methodically without much confusion for the patient or her family. Observation of the patient over the course of TOLAC may result in a constellation of signs and symptoms that will raise suspicion for impending or actual uterine rupture. As a result, continuity of care and detailed communication among those managing the patient is essential.

Contraindications & relative contraindications to TOLAC

Absolute contraindications to any vaginal delivery, either spontaneous or VBAC, make patient counseling relatively easy and a plan for ERCD readily implemented. Some of the absolute contraindications to vaginal delivery, including VBAC, are listed in Box 2 [6,7]. In particular, patients with a prior fundal uterine incision (i.e., involvement of the contractile portion of the uterus), prior classical or ‘T’ uterine incision have a higher rate of uterine rupture and are poor candidates for a planned TOLAC [7]. In addition, case series have reported a risk of recurrent uterine rupture of 6% for uterine scars confined to the lower uterine segment with recurrent rupture rates as high as 32% for scars that extend into the fundus [16,17]. These patients are at exceptionally high risk for complications and should be strongly counseled against TOLAC. However, there are situations when a patient with an absolute contraindication presents in advanced labor, and re-evaluation of mode of delivery is required. In these cases, the balance of risks and benefits should be considered and proceeding with TOLAC may be acceptable [6]. Time permitting, we try to adhere to the original plan of ERCD as this usually leads to less confusion for all involved.

Certain scenarios alter the risk: benefit balance for TOLAC and deserve special discussion. These ‘relative contraindications’ may involve more discussion between the patient and the obstetrician, and a decision may not be easily reached. The first involves a previous low vertical uterine incision. Women with a previous low vertical incision have reported rates of successful VBAC similar to those undergoing a TOLAC after LTCD [18 –21]. They also do not appear to have an increased risk of uterine rupture or maternal and perinatal morbidity [6]. There is considerable subjectivity, however, in determining whether a vertical incision goes into the contractile portion of the uterine muscle, or ‘active segment’. In a best-case scenario, an available operative report from the prior CD contains a detailed description of the incision or the surgeon's impression of whether the incision involved the active segment.

If there is any uncertainty regarding the type of prior uterine incision, we err on the side of caution and recommend ERCD. When considering an unknown type of previous uterine incision, two case series reported rates of uterine rupture similar to those in women with documented LTCD. Another study evaluating risk factors for uterine rupture found no significant association with the presence of an unknown scar [10,22,23]. Because most CDs are LTCDs and the type of uterine incision can usually be inferred based on the indication for the previous CD, TOLAC is not absolutely contraindicated [6]. In our practice, we rely heavily on the indication and gestational age of the prior CD before making a recommendation. If this information is uncertain, we generally recommend ERCD unless the patient has had a successful VBAC.

Box 2.

Absolute contraindications to trial of labor after cesarean.

Placenta previa

Placenta accreta

Vasa previa

Funic presentation

Transverse lie

Higher order multiples (triplets and above)

Prior fundal uterine incision

Prior uterine rupture

Uterine distortion

Obstructive maternal pelvic lesions

Fetal Ehlers–Danlos type IV

Another scenario involves fetal macrosomia, defined as an estimated fetal weight (EFW) of >4500 g. Women attempting TOLAC with an EFW of &ge4000–4500 g have a lower success rate for VBAC when compared with women without a macrosomic fetus [24 –27]. In 2003, Elkousy et al. reported that uterine rupture risk is increased (RR: 2.3; p < 0.001) for women undergoing TOLAC without a history of a prior vaginal delivery and neonatal birth weights greater than 4000 g [27]. In 2006, Peaceman et al, using the Maternal–Fetal Medicine Units Network Cesarean Registry, focused on subjects whose prior CD was performed for labor dystocia, defined as a failed induction, cephalopelvic disproportion (CPD), failure to progress or failed forceps or vacuum [28]. VBAC success in these subjects was 54% if the previous CD was performed for labor dystocia, compared with a success rate of 67% for other indications. The success rate was further reduced if the EFW of the pregnancy attempting VBAC exceeded the initial pregnancy fetal weight by 500 g (38%) [28]. Furthermore, the likelihood of achieving a successful VBAC with a previous history of labor dystocia is consistently lower (40–70%) [12,29].

If a woman is diabetic and the fetus is macrosomic on antenatal ultrasound, it is reasonable to counsel against TOLAC and recommend ERCD for best maternal–fetal outcome, even though the EFW may be unreliable in this setting. Similarly, for a woman who is not diabetic and the EFW is >5000 g, regardless of prior route(s) of delivery, it is reasonable to recommend ERCD over TOLAC. For those women whose fetus measures 4500–5000 g, regardless of whether or not the mother is diabetic, we have a lower threshold for proceeding to ERCD based on failure to progress in labor if the choice has been made to proceed with TOLAC. In this scenario, TOLAC can be attempted with close observation of the labor curve. Finally, a ‘contracted pelvis’ on clinical exam with or without macrosomia is a relative contraindication to TOLAC [12]. Overall, it is necessary to consider birthweights, modes of delivery and complications encountered (e.g., dystocia) in past deliveries together with the EFW of the current pregnancy to determine if TOLAC is acceptable.

Finally, whether women with two previous CDs are candidates for TOLAC is debatable. The greatest concern for these patients is an increased risk of uterine rupture and maternal–fetal morbidity. While the risk of uterine rupture during TOLAC in patients with one prior LTCD is commonly cited as 0.5–1%, and in some reports as high as 1.7%, the risk in women with more than one previous CD is reported to be anywhere between 0.9 and 3.7% [2,30 –37]. Data on composite maternal morbidity in TOLAC and VBAC with two prior CDs is even more variable. In 2005, Macones et al. examined outcomes in women with one prior LTCD who attempted VBAC compared with those with two prior CDs who attempted VBAC or opted for an ERCD [30]. In this study, the reported rate of VBAC success was similar in women with one prior LTCD (75.5%) compared with those with two prior CDs (74.6%), though the odds of major morbidity were higher in the latter group (adjusted odds ratio [OR]: 1.61; 95% CI: 1.11–2.33) [30]. In addition, among women with two prior CDs, those who opted for TOLAC had higher odds of major complications compared with those who opted for ERCD (adjusted OR: 2.26; 95% CI: 1.17–4.37), although the absolute risk remained low [30].

Similarly, in a study by Landon et al., maternal and perinatal outcomes were compared among women attempting vaginal birth after multiple CDs and those with a single prior LTCD, and outcomes for women with multiple CDs undergoing trial of labor (TOL) were compared with those choosing ERCD [36]. They found that uterine rupture occurred in 0.9% of women (n = 975) with multiple prior CDs compared with 0.7% of women (n= 16,915) with a single LTCD (p = 0.37). Although a history of multiple CDs was not associated with an increased risk for uterine rupture, the rates of hysterectomy (0.6 vs 0.2%, p = 0.023) and transfusion (3.2 vs 1.6%, p < 0.001) were increased when compared with women with a single prior CD attempting TOLAC. Finally, a composite of maternal morbidity was increased in women with multiple prior CDs compared with those having ERCD (OR: 1.41; 95% CI: 1.02–1.93), but the absolute risk for complications was small. They concluded that TOL after multiple CDs should remain an option for eligible women [36].

A recent meta-analysis by Tahseen and Griffiths looked at success rates of VBAC after two CDs and associated adverse maternal–fetal outcomes [37]. In patients undergoing TOLAC after two prior CDs, they found the following rates: VBAC success 71.1%, uterine rupture 1.36%, hysterectomy 0.55%, febrile morbidity 6.03% and blood transfusion 2.01%. The success rate of VBAC after two prior CDs (71.1%) was lower than after one prior CD (76.5%), and the adverse maternal outcome rates after two prior CDs were higher than after one prior CD, although the absolute rates were small. In addition, the adverse maternal outcomes of TOL after two prior CDs were similar to ERCD (third cesarean) when comparing hysterectomy, blood transfusion and febrile morbidity. They also found higher success rates and lower uterine rupture rates in women with two prior CDs if they had a history of a successful vaginal delivery. They concluded that women who request a TOL after two CDs should be counseled carefully and have the option of TOLAC [37].

It appears that the success rate of TOLAC after two previous CDs is comparable to that for one prior CD, and the morbidity is increased with VBAC after two prior CDs when compared with one prior CD and is similar to that of ERCD. If the patient has previously delivered vaginally, the chance is greater for safe undertaking of TOLAC and VBAC success. The risk of uterine rupture is low overall, even in women with more than one prior CD. ACOG agrees that TOLAC can be offered to women with two prior CDs after counseling and identification of factors that affect their probability of successful VBAC [6]. In our practice, having as much information as possible on the two prior CDs is crucial for counseling on TOL. If there are large information gaps or additional factors that render the patient a poor candidate for TOLAC, we will recommend ERCD. In addition, if she does not desire future fertility, we will offer ERCD with tubal ligation. In general, if the patient has had a successful VBAC and is in spontaneous labor, and we have adequate information on the two prior CDs, we will consider allowing TOLAC if the patient desires. Finally, owing to a lack of evidence, we do not induce women with two CDs.

Risks & morbidity of TOLAC & VBAC

The risks of TOLAC and VBAC are well documented with the risk of uterine rupture justly garnering the most consideration. ACOG defines a risk of 4–9% if the incision involves the contractile portion of the uterus, including classical and inverted ‘T’ incisions [6,38]. Maternal morbidity includes bladder, bowel and vascular injury that occurs due to uterine rupture itself [2,39]. Variables adding to the severity and sequelae of uterine rupture include the size and location of the rupture and degree of fetal umbilical cord compression [12]. Although the area of prior uterine incision most commonly ruptures, this may extend anywhere on the uterus and into the broad ligament or bladder. Such extensive rupture may cause massive maternal blood loss and hysterectomy. If the uterine rupture involves the placenta, causes umbilical cord compression or results in fetal extrusion the fetal outcomes are more severe [9,12]. In the 2010 ACOG Practice Bulletin on VBAC, it was reported that women with at least a 60–70% chance of VBAC have equal or less maternal morbidity when they undergo TOLAC than women undergoing ERCD, and women who have a <60% probability of VBAC have a greater chance of morbidity than woman undergoing ERCD 1,6,40].

Factors that increase the risk of uterine rupture are listed in Box 3 [6]. In 2011, Barger et al. identified risk factors associated with uterine rupture among term pregnancies attempting a VBAC after a prior LTCD [41]. They found that previous successful VBAC decreased the risk for uterine rupture, and gestation >40 weeks and macrosomia increased the risk. In addition, oxytocin for induction increased the risk by two-to three-times from a baseline of 0.5% to 1.0–1.5%, with a slightly lower effect when used for augmentation. Finally, Mercer et al. estimated the risk of VBAC stratified by the number of prior successful VBACs [42]. Investigators found that the rate of uterine rupture decreased after the first successful VBAC and did not increase with subsequent vaginal deliveries (0.87% risk after VBAC, 0.52% after five deliveries), supporting the idea that multiple VBACs do not weaken the lower uterine segment. In addition, an increasing number of prior VBACs is associated with a greater probability of VBAC success and a lower risk of uterine rupture and perinatal complications [42]. In 2011, Scifres et al. identified risk factors for major maternal morbidity in women attempting VBAC and attempted to develop a model to predict major maternal morbidity [43]. Those women who experienced at least one complication of a composite adverse outcome (e.g., uterine rupture, bladder/ureteral injury, bowel injury or uterine artery laceration) were identified (300 out of 13,706 or 2.1%). They found that prior abdominal surgery, augmentation of labor (AOL) and induction of labor (IOL) were associated with an increased risk of the composite outcome. Their multivariate model that combined maternal characteristics with variables linked to VBAC success or failure could not, however, accurately predict major maternal morbidity [43]. In addition, there was a 60% increase in major maternal morbidity in women with a history of prior abdominal surgery who underwent TOLAC, which may have been attributable to postsurgical adhesions. They also found that a prior vaginal delivery was associated with a decreased risk for major maternal morbidity [43].

One fact that strongly supports TOLAC and VBAC is the increased incidence of placenta previa and accreta with each subsequent CD [44,45]. Placenta previa with accreta and repeat CD is extremely challenging to manage and can result in severe hemorrhage, emergency hysterectomy, bladder and bowel injuries and maternal death [12]. The absolute risk of previa associated with any number of CDs is 12 per 1000 (95% CI: 8–15 per 1000; p < 0.001) [5]. The incidence with each additional prior CD increases from 0.01% with one prior CD (95% CI: 6–13 per 1000) to 28% (95% CI: 18–37 per 1000) with three or more CDs [5]. The incidence of placenta accreta in women with previa also increases with each successive CD. Two studies have shown that the presence of placenta previa increased the probability of accreta from 3.3 to 4% in women undergoing their first CD to 50–67% in women with four or more prior CDs [46]. More notably, women with three or more prior CDs and previa more often required hysterectomy [47 –50]. Overall, the risk of placenta previa, accreta and hysterectomy increases in a dose–response fashion with serial CDs [46]. As a result, when evaluating the risks of TOLAC versus ERCD, one has to include the risks to future pregnancies.

Box 3.

Factors that increase risk of uterine rupture in women undergoing trial of labor after cesarean.

Excessive oxytoxin usage

Labor dystocia

Three or more prior CDs

Multiparity

Macrosomia^†

Prior nonpregnant uterine surgery or perforation

In summary, when counseling the patient, the first approach should be to acknowledge any immediate contributors to risk for uterine rupture and potential maternal–fetal morbidity. When considering the macrosomic fetus or the fetus at >40 weeks gestation, in our practice, the labor curve is followed very closely and the threshold is lowered for proceeding to repeat CD if necessary. If a patient has a history of extensive abdominal surgery, consideration must be given to the scenario where an emergent CD is necessary and an extended amount of time may be needed in order to reach the fetus, as this can be detrimental to the fetus. In addition, the risk associated with general anesthesia in the absence of adequate regional anesthesia contributes to the overall morbidity of an emergent CD. If we feel that a controlled ERCD would provide the best maternal–fetal outcome despite a history of extensive abdominal surgery, we will recommend ERCD in order to avoid an emergent CD in the face of a failed TOLAC. In our practice, if there are one or more ‘red flags’ that would alter the risk: benefit of a TOLAC or if a patient does not desire future fertility, ERCD will be recommended.

Who is the best VBAC candidate?

The best candidate for TOLAC and VBAC is a patient in whom the maternal–fetal risks are minimized, the likelihood of success is maximized and the balance between the two is acceptable to the patient and clinician [46]. Counseling of the patient should involve four elements: her chance of success, risk of uterine rupture and subsequent morbidity to her and/or her fetus, any additional morbidities that may increase risk to her and/or her fetus as a result of her medical/surgical history and her personalized risk with ERCD. In addition, consideration for future fertility plans should also be discussed, as maternal morbidity increases with each subsequent CD and neonatal morbidity increases with TOLAC [6].

Box 4.

Predictors of successful vaginal birth after cesarean.

Previous vaginal delivery (including VBAC) [2,6,7,45,51 –57]

Spontaneous labor [6,7,51,53]

Cervical dilatation and/or effacement [45,56,57]

Nonrecurring indication for prior CD (e.g., breech and fetal ‘distress’) [6,7,51]

Epidural usage [51]

Important predictors for a successful TOLAC and VBAC are listed in Box 4 [2,6,7,45,51 –57]. After examining factors that influence the success of TOLAC and subsequent VBAC, Landon et al. found that women with a cervical dilation of ≥4 cm at admission had a greater likelihood of achieving a successful TOL when compared with women with a failed TOLAC (48.1 vs 26.4%, p < 0.001) [51]. More notably, spontaneous labor and advanced cervical dilatation at the time of labor or at rupture of membranes are both significantly associated with a decreased risk of uterine rupture [58]. Furthermore, Gonen et al. found that the presence of cervical dilatation at the onset of labor significantly increased the likelihood of achieving vaginal birth (OR: 2.5; 95% CI: 1.3–4.9) in a study of 475 women who had a prior CD [56]. Cervical effacement in spontaneous labor or at the time of induction is also positively associated with the chance of a successful VBAC [58]. When a patient who may not have been considered the ideal candidate presents in spontaneous labor with cervical dilation, her likelihood of successful VBAC is altered and proceeding with TOLAC may be acceptable.

When considering women with a prior VBAC, the probability of subsequent successful VBAC has been reported to be as high as 94% [29]. As mentioned previously, Mercer et al. estimated the success rates of VBAC stratified by number of prior successful VBACs and found that the VBAC success rate increased with increasing numbers of prior VBACs (63.3, 87.6, 90.9, 90.6 and 91.6% for 0, 1, 2, 3 and 4, respectively) [42]. For those women who had a successful vaginal delivery before the index CD, the probability of achieving a successful VBAC is 83% compared with women without a history of a prior vaginal delivery (65%) [29]. In addition, a recent meta-analysis examining predictors of VBAC success reported that prior vaginal delivery increases the odds of VBAC by more than threefold (OR: 3.41; 95% CI: 2.56–4.54) [59]. The circumstances surrounding a prior successful vaginal delivery or VBAC are vital to counseling for the current TOLAC. Although these factors are important predictors of a successful VBAC, on their own they cannot decide whether an individual patient is a candidate for TOLAC or will have a successful VBAC.

There are additional factors that increase the chance of a successful VBAC. If the first CD was a result of a nonrecurring indication (i.e., fetal distress, abruption, breech, among others), the likelihood of a successful VBAC is increased as compared with a recurring indication such as labor disorders or CPD [29,60 –64]. The probability of VBAC has been reported to be approximately 75% when the CD was performed for nonrecurring indications [5,59,65 –67]. In 2011, Madaan et al. conducted a study on 300 women with one prior CD who were candidates for TOL in order to examine predictive factors and TOL outcomes [68]. They reported a TOLAC success rate of 53.6%, with favorable Bishop score, spontaneous onset of labor and history of previous VBAC being significantly associated with successful VBAC. In addition, higher chances of VBAC were found with breech as an indication of previous CD (67.1%) as compared with nonprogression of labor or failed induction as an indication (39%). Finally, prior LTCD, no previous uterine surgery or history of uterine rupture, an adequate pelvis, a normal fetal size and a readily available physician and ancillary staff/support resources (i.e., anesthesia and blood products) are factors that are associated with an increased likelihood of successful VBAC [12].

Conversely, several factors are associated with a decreased chance a successful VBAC (Box 5). First, a shorter interdelivery interval has been associated with a reduced chance of achieving VBAC and a potentially increased risk of uterine rupture [33,69,70]; ideally, a waiting period of between 18 and 24 months is recommended before attempting TOLAC [71,72]. Next, although several studies have reported decreased VBAC rates in women attempting TOLAC at >40 weeks of gestation, there is no consensus on whether uterine rupture rates are increased in this population [73 –76]. In general, as gestational age increases, the likelihood of VBAC is decreased, particularly when the pregnancy progresses >4l weeks of gestation [46,59]. Increasing maternal age has also been associated with a decreased chance of successful VBAC. In 2007, Srinivas et al. estimated the effect of maternal age on VBAC success [77]. Using the age range of 21–34 years as a reference group, women older than 35 years of age were more likely to experience an unsuccessful TOL (OR: 1.14; 95% CI: 1.03–1.25) and were 39% more likely to experience complications during TOLAC [77]. Furthermore, women older than 40 years of age had almost half the likelihood of successful VBAC in a meta-analysis (OR: 0.53; 95% CI: 0.32–0.86) when compared with women under 40 years of age [59].

Another factor associated with decreased VBAC success is maternal obesity. Durnwald et al. found the VBAC success rate in 510 obese and overweight women with one prior CD who attempted a TOLAC to be 66% (337 out of 510), and the success rate was significantly lower for women with a BMI >30 (54.6%; p = 0.003) compared with women with a normal BMI (70.5%) [78]. Similarly, Landon et al. found the overall VBAC success rate in obese women (BMI >30) was 68.4%, compared with a rate of 79.6% in nonobese women (p < 0.001) [51]. Finally, as previously discussed, recurring indications for the index CD are negatively associated with successful VBAC. The probability of achieving VBAC is lower (~54%) if the prior indication for CD was related to CPD and labor abnormalities such as progress/active phase arrest, labor dystocia or arrest of descent, and the likelihood of VBAC is approximately 60% if fetal intolerance of labor/fetal distress was the reason for the prior CD [5,46,59]. However, the greatest morbidity occurs when an unsuccessful TOLAC is followed by a repeat CD. As a result, when any one of the factors that decrease the chance of successful VBAC are present, but are not contraindications to TOLAC, we counsel the patient that while TOLAC is possible, she must be prepared if these factors prevent her from achieving a VBAC. We closely monitor the labor curve with the goal of achieving delivery, if possible, in a timely fashion in order to minimize maternal–fetal morbidity.

Identifying the ‘ideal’ VBAC candidate is subjective and not only relies on how the literature and current data defines the best candidate, but also depends on physician preferences and their willingness to offer a TOLAC. Although predictive models, algorithms and online calculators exist that incorporate factors that are positively associated with successful VBAC and provide individual risk assessments, the results are widely variable [7].

Box 5.

Predictors of failed vaginal birth after cesarean.

Short interdelivery interval (<18–24 months) [69]

Advanced maternal age (>35 years of age) [6,13,59,77]

Maternal obesity (BMI >30) [6,13,51,78]

Gestational age (>40–41 weeks) [6,13,46,59]

Increasing EFW (>4000–4500 g) [13,24,25,27]

Increased EFW from index CD (+500 g) [28]

Contracted pelvis on clinical exam [12]

Comorbid medical/surgical conditions [6,70]

Recurring indication for prior CD (e.g., CPD and labor abnormalities) [5,6,13,46,59]

Labor induction [13,33,47,69]

IOL & VBAC

Although IOL is associated with lower VBAC success rates when compared with spontaneous labor, it is not contraindicated with rates of successful VBAC between 51 and 80% [47,51,73,79 –84]. In the study previously mentioned by Madaan et al., the success of TOLAC in women having spontaneous labor was 57.8%, significantly higher than the 38% success rate in the induced group [68]. In 2005, Landon et al. found that IOL of any type was associated with a 50% reduction in the chance of achieving a successful vaginal birth (OR for successful VBAC: 0.50; 95% CI: 0.45–0.55) [51]. Grobman et al. in 2007 found that women who required IOL were less likely to achieve vaginal birth compared with women who entered labor spontaneously (51 vs 65%; p < 0.001) [47]. Furthermore, in women with a previous vaginal birth who underwent TOLAC with induction, there was a statistically significant reduction in success compared with spontaneous onset of labor (83 vs 88%; p < 0.001) [47]. TOLAC may be favored due to pregnancy complications, patient preference or increased risk of ERCD [82,85]. However, even when induction is chosen, there is still no consensus on which method of induction is the safest or most effective.

Data on whether cervical effacement and dilation has an association with successful VBAC in the setting of induction are conflicting and limited. In a retrospective cohort study, Bujold et al. evaluated the outcomes in 685 women who had a previous CD and required IOL [86]. The chance of successful VBAC was significantly correlated with a modified Bishop score of >six at the time of induction increasing the likelihood of vaginal birth (adjusted RR: 2.07; 95% CI: 1.28–3.35) [86]. On the other hand, a low Bishop score necessitating cervical ripening or IOL in the presence of an unfavorable cervix reduces the chance of vaginal birth while increasing the chance of CD [47,83]. It appears that cervical status at the time of IOL for VBAC is not definitively associated with success or failure of TOLAC, although an unfavorable cervix may decrease the likelihood to the greatest degree [47,83,86]. Regardless, favorability of the cervix at time of induction should be considered and should be an essential component in the counseling of the patient. In our practice, a favorable cervix is considered heavily when proceeding with IOL.

The biggest concern with IOL for VBAC is a further increased risk of uterine rupture beyond that already associated with TOLAC. An increased risk of uterine rupture after IOL is consistently reported in the literature with rates greater in IOL (1.4–2.3%) compared with those who are in spontaneous labor (0.45–0.7%) [73,81,84]. In the study by Madaan et al., the rate of uterine rupture in the spontaneous labor group was 0.8% as compared with 3.1% in the induced group [68]. Although ACOG supports IOL for maternal and fetal indications for TOLAC, there is no consensus on which method of induction is safest with regard to uterine rupture. In 2001, Lydon-Rochelle et al. reported that the risk of rupture was 0.52% if labor occurred spontaneously compared with a risk of uterine rupture of 0.77% if labor was induced without prostaglandins (PGs) and 2.45% if induced with PGs in women with a single prior CD [21]. In a multicenter study by Landon et al. AOL or IOL was associated with an increased risk of uterine rupture compared with spontaneous labor (0.4% for spontaneous labor, 0.9% for augmented labor, 1.1% for oxytocin alone and 1.4% for induction with PGs with or without oxytocin) [2]. A secondary analysis from this study showed that in women with one prior LTCD, there was an increase in uterine rupture only in those undergoing induction who had no prior vaginal delivery (1.5 vs 0.8%; p = 0.02), and there was no association with favorable or unfavorable cervix at the time of IOL and uterine rupture [47]. Conversely, Weimar et al. reported that a low Bishop score necessitating cervical ripening was a risk factor for uterine rupture [87]. Oxytocin and PGs as methods of induction are discussed below.

Oxytocin can be used for IOL or AOL in women with a prior CD. It appears that whether oxytocin is used for IOL or AOL, the chance of successful VBAC is reduced. Eden et al. in 2010 reported a reduction of 48% in the chance of successful VBAC after the use of oxytocin for AOL (OR: 0.52; 95% CI: 0.33–0.82) [59]. Guise et al. in 2010 reported that in studies examining the use of oxytocin as an induction agent, the estimated probability of VBAC was 62% (95% CI: 53–70%), and as an augmentation agent, the probability of VBAC was similarly decreased at 68% (95% CI: 64–72%) [5]. The association of oxytocin for IOL or AOL with uterine rupture as reported in the literature is variable. In 2004, Landon et al. reported a threefold increase in the risk of uterine rupture when labor was induced with oxytocin alone compared with spontaneous onset of labor (OR: 3.01; 95% CI: 1.66–5.46; p < 0.001) [2].

In contrast, Macones et al. in 2005 reported that oxytocin use alone for IOL was not associated with an increase in the risk of uterine rupture [39]. It is unclear whether an increased risk of uterine rupture with IOL also applies to oxytocin used for AOL. Oxytocin augmentation has been reported to increase the risk of uterine rupture by a factor of almost 2.5-times in some studies [2,59]. The maximum dosage of oxytocin that should be used during IOL is unknown, with some studies showing that higher doses of oxytocin increase the risk of uterine rupture [12]. In addition, the effect of oxytocin dose, the regimen used and the duration of administration during labor must also be considered [58]. In a 2008 study by Cahill et al., examining the association between maximum oxytocin dose and the risk of uterine rupture in women with a history of previous CD, a dose–response effect with increasing risk of uterine rupture with higher maximum doses of oxytocin was found [88]. In this study, oxytocin administered at more than 20 mU/min increased the risk of uterine rupture by at least fourfold (21–30 mU/min; hazard ratio: 3.92; 95% CI: 1.06–14.52).

The use of PGs for IOL for VBAC is not universally supported by the literature, particularly when concerning the risk of uterine rupture. The only definitive consensus at this time is that misoprostol (PGE₁) is contraindicated for IOL owing to studies showing an increased risk of uterine rupture in women with a prior CD or significant uterine surgery. Most studies on the use of PGs for IOL in VBAC involve the use of PGE₂, and the use of PGs is associated with an increased risk of uterine rupture. In 2005, Smith et al. studied more than 36,000 women who had a prior CD, of whom 4600 underwent PG induction for TOLAC [89]. In this study, the reported risk of uterine rupture and subsequent perinatal death after PG induction was 11 per 10,000 labors compared with 4.5 per 10,000 labors in the absence of PG induction [89]. Furthermore, among women with a predicted CD risk of <20%, the incidence of uterine rupture was 2.0 (95% CI: 1.1–3.2) per 1000 and among women with a CD risk of >40%, the incidence was 9.1 (95% CI: 6.4–12.6) per 1000.

Finally, IOL with PGs was associated with almost a 50% increase in a woman's chance of emergency CD when compared with those whose labor was not induced (OR: 1.42; 95% CI: 1.26–1.60; p < 0.001) [89]. When considering PG induction followed by augmentation with oxytocin, current data do not support the sequential use of the two agents due to an increased risk of uterine rupture (adjusted OR: 3.07; 95% CI: 0.98–9.88) [39]. At our institution, until more data are reported on the safety of PG, we do not use PG during IOL for TOLAC; instead, we use oxytocin for IOL and AOL. In our practice, we use oxytocin at a rate of ≤20 mU/min and follow the labor curve closely.

Conclusion

Despite the fact that consensus panels have recommended that TOLAC and VBAC are a safe alternative to ERCD, the CD rate remains high and physicians are less likely to offer TOLAC for a number of reasons. The main reason is owing to the fear of uterine rupture. It is potentially a catastrophic event with poor outcomes for the mother and/or fetus. As a result, our efforts to choose the best candidate for TOLAC and the decision of whether or not to induce during TOLAC are guided by our assessment of the potential for uterine rupture. What we must keep in mind, however, is that what is best for the woman may not be best for the fetus/neonate. Because ERCD is associated with a lower neonatal morbidity overall when compared with TOLAC, the decision on whether a woman is a candidate for VBAC principally rests on what will result in the lowest morbidity for both mother and fetus. Because predictive models are not completely reliable at choosing who has the best potential for a successful VBAC and who has the lowest risk, choosing the appropriate candidate is a joint effort on the part of the patient and physician.

Future perspective

At this time, the goal put forth by consensus panels is to observe a decrease in the rate of CDs by both encouraging and providing access to TOLAC. However, we cannot ignore the effect that healthcare institutions and third-party payer policies, in addition to the influence of the medico–legal community, have on the availability of TOLAC and VBAC. Therefore, continued advocacy on the part of the obstetrician is essential in order to swing the pendulum. Patient counseling should be based on absolute – not relative – risks and access to centers allowing TOLAC should be improved, with the decision ultimately in the hands of the woman. Unfortunately, we do not envisage factors such as increasing maternal obesity, increasing maternal age with concomitant medical–surgical complications, and data showing that fetal morbidity and mortality are decreased with ERCD, resulting in a decrease in CDs to a degree that is acceptable to consensus panels. At the moment, concern for increased fetal risk and uterine rupture with TOLAC will continue to swing the pendulum towards ERCD. Although this article focused on TOLAC and the maternal risk: benefit, the fetal risk: benefit may indeed be what ultimately guides the standards of care when considering TOLAC versus ERCD.

Executive summary

Background

Vaginal birth after cesarean (VBAC) delivery is considered a safe alternative to elective repeat cesarean delivery (CD) with between 60 and 80% of attempts at VBAC resulting in a successful vaginal birth.

Signs of uterine rupture

Because the most common sign associated with uterine rupture is an abnormal fetal heart rate tracing (up to 70% of cases), continuous fetal heart rate monitoring during labor is recommended.

Contraindications & relative contraindications to trial of labor after cesarean delivery

Patients with a prior fundal uterine incision (involvement of the contractile portion of the uterus), prior classical or ‘T’ uterine incision have a higher rate of uterine rupture and are poor candidates for a planned trial of labor after cesarean (TOLAC) delivery.

Risks & morbidity of TOLAC & VBAC

The increased incidence of placenta previa and accreta with each subsequent CD is a factor in counseling on TOLAC, as the scenario of placenta previa with accreta and repeat CD is extremely challenging to manage and can result in severe hemorrhage, emergency hysterectomy, bladder and bowel injuries and maternal death.

Who is the best VBAC candidate?

The best candidate for TOLAC and VBAC is a patient in whom the maternal and fetal risks are minimized, the likelihood of success is maximized and the balance between the two is acceptable to the patient and clinician.

Women with a history of a prior VBAC and an index CD performed for a nonrecurring indication have an increased probability of subsequent successful VBAC.

Although predictive models, algorithms and online calculators exist that incorporate factors that are positively associated with successful VBAC and provide individual risk assessments, the results are widely variable.

Induction of labor & VBAC

Although induction of labor is associated with lower VBAC success rates and increased risk of uterine rupture when compared with spontaneous labor, it is not contraindicated and is associated with a rate of successful VBAC between 51 and 80%.

Footnotes

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

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