For most of this century, routine repeat cesarean was the rule in the United States. Prior to 1970, almost every North American hospital maintained the policy that all women who underwent a cesarean delivery would have a repeat cesarean operation for any and all subsequent births. This practice dates back to an article published in 1916 which contained the now-famous phrase, “once a cesarean, always a cesarean.”¹ Interestingly, the purpose of that article was actually to stress the risks of the cesarean operation, and the “once a cesarean” phrase was clearly meant to emphasize that one of the risks of a primary cesarean was that a dangerous repeat operation might be required. In that era, primary cesarean was performed via the “classical” uterine incision, which extended up vertically from the lower uterine segment to the fundal region of the uterus. Use of the classic cesarean incision began to decline after the low transverse uterine incision was pioneered by Kerr in the mid-1920s.^1A Fortunately, the risk of uterine rupture during labor following a low transverse cesarean is approximately 10 times lower than that during labor following a classical cesarean. During the 1960s and 1970s, several studies concluded that vaginal birth after cesarean (VBAC) was a reasonable option.² In the 1980s, larger studies confirmed this conclusion.^3,4 In response to these results, many obstetricians abandoned the old dictum and offered the option of VBAC to appropriate patients. The vaginal delivery rate among pregnant women with prior cesareans (VBAC rate) in the United States increased from 3.5% in 1980 to almost 25% by 1993. This implies that almost one half of all pregnant women with a prior cesarean delivery were opting for a trial of labor by 1993.

Maternal Risks

In a large study comparing trial of labor to elective repeat cesarean, hospital length of stay, incidence of postpartum transfusion, and incidence of postpartum fever were, surprisingly, found to be higher in the elective repeat cesarean group.⁵ However, this was due to the fact that 75% of patients in the trial of labor group delivered without requiring a cesarean operation. When elective repeat cesarean is compared with cesarean section performed after a failed trial of labor, maternal morbidity is indeed higher in the failed trial of labor group.⁶ Hysterectomy is required in approximately 10% of uterine rupture cases. Fortunately, maternal death is exceedingly rare with either elective repeat cesarean or trial of labor. In the two largest multicenter studies on VBAC, only one rupture-related maternal death occurred in more than 20,000 trials of labor.^3,5,7 Maternal deaths due to uterine rupture have been reportedduring attempted home births in areas where in-hospital VBAC was not readily available.

Fetal Risks

In the 99% of trials of labor that do not result in uterine rupture, neonatal outcome is comparable to that of patients who give birth through labor who have had no prior uterine surgery. However, in the 1% of trials of labor that are complicated by uterine rupture, fetal injury or death may occur, even with fairly rapid intervention. Perinatal outcome with uterine rupture has been linked to the time interval from the onset of ominous fetal heart rate patterns to delivery of the infant. A large study on uterine rupture found that no infants had significant perinatal morbidity when delivered within 17 minutes of the onset of a prolonged deceleration.⁸ When this interval was longer than 17 minutes, several infants suffered permanent neurologic injury or death. The incidence of asphyxia-related fetal neurologic injury due to uterine rupture is approximately 1 in 2500 to 1 in 5000 trials of labor.^3,5,8 It should be noted that most VBAC studies were conducted in medical centers with 24-hour in-house obstetricians and anesthesiologists. Thus, although the incidence of uterine rupture may be similar in other settings (~1%), the perinatal outcomes may be less favorable. The potential for these rare but catastrophic outcomes must be considered when weighing the risks versus the benefits of VBAC.

Maternal Benefits

Trial of labor, when successful, eliminates the need for cesarean delivery and thus avoids the potential risks associated with major surgery. Studies performed in the 1970s concluded that the risk of maternal death was up to 25 times higher with cesarean delivery than with vaginal birth.⁹ Although these studies may have been biased by inclusion of more complicated cases in the cesarean cohort, thus exaggerating the risks of cesarean birth, most experts today agree that maternal morbidity and mortality are at least slightly increased by cesarean delivery. A significant benefit of VBAC is the avoidance of multiple repeat cesarean operations, which have been clearly linked to potentially fatal placenta previa accreta. In the United States, the incidence of placenta accreta increased approximately 10-fold as the cesarean rate quadrupled. When placenta previa is present with no previous uterine incision, the risk of accreta is 1% to 5%. However, the risk increases dramatically (to as high as 40%) in women with two prior cesareans.¹⁰ Furthermore, VBAC generally results in a shorter hospital stay and a quicker recovery.

Perinatal Benefits

Some doctors feel that elective repeat cesarean is essentially risk-free for the baby and therefore believe that VBAC offers no potential neonatal benefits. This is apparently not correct. Iatrogenic prematurity associated with elective repeat cesarean, a serious problem in the 1960s and 1970s, was partially eradicated with the advent of early ultrasound dating and fetal lung maturity testing. However, despite widespread dissemination of management guidelines for the timing of elective repeat cesareans, this problem has not been completely eliminated. One recent study found that 1.5% of infants delivered by elective repeat cesarean were admitted to the neonatal intensive care unit (NICU) with serious respiratory difficulty.¹¹ Several of these infants required mechanical ventilation, and the average NICU stay was 11 days. Even more worrisome is the occasional occurrence of extremely severe neonatal respiratory failure after elective repeat cesarean with no evidence of iatrogenic prematurity. Eighteen percent of infants referred to two major University NICUs for extracorporeal membrane oxygenation (ECMO) therapy were products of elective repeat cesareans at term.¹² Of 242 infants requiring ECMO, 40 had been delivered by elective repeat cesarean, and 4 had been delivered by elective cesarean for breech. The criteria for ECMO initiation (PaO₂ < 50 for >2 hours or PaO₂ <60 for >8 hours despite maximum ventilator support) were consistent with an 80% probability of neonatal death. The authors concluded that life-threatening respiratory distress following elective repeat cesarean delivery is a problem of significant proportions. These cases occur very infrequently but can have catastrophic outcomes and thus must be considered when weighing the risks versus benefits of elective repeat cesarean. Finally, successful VBAC also allows the mother to interact with her newborn immediately and may facilitate the maternal-infant bonding process.

Uterine Rupture Versus Dehiscence or Uterine Window

The main risk of VBAC is uterine rupture. Rupture of the unscarred uterus does occur, but it is a very uncommon event. True or complete uterine rupture must be differentiated from a thinning of the uterine wall that is often termed uterine Dehiscence, thin lower segment, or uterine window. Such thinning occurs much more frequently than complete rupture but is generally inconsequential. In contrast, complete uterine rupture involves all layers of the uterine wall, including the serosa (with or without fetal extrusion) and carries significant maternal and fetal risks. Complete uterine rupture occurs in approximately 1% of patients undergoing trial of labor with a low transverse uterine scar. Complete uterine rupture is associated with partial or complete fetal extrusion in about 50% of cases. The term catastrophic uterine rupture is often applied to cases of complete uterine rupture that result in poor fetal or maternal outcome.

Uterine Rupture With Prior Classical or Low Vertical Uterine Incisions

The risk of uterine rupture is as high as 10% for the patient with a prior classical uterine incision. For this reason, trial of labor is generally felt to be contraindicated in women with a prior classical cesarean scar. It is reassuring to remember that in the United States and many other industrialized nations, the classical uterine incision has become quite uncommon. In contrast, a prior low vertical uterine incision appears to carry a risk of rupture only slightly higher than that of a prior low transverse incision. However, because the line of demarcation between a low vertical and a classical uterine incision is not always clear, many obstetricians do not recommend trial of labor with a prior low vertical uterine incision.

Uterine Rupture with Unknown Type of Prior Uterine Incision

A common situation in clinical practice involves the obstetric patient with an unknown type of uterine scar. If the primary cesarean was performed in the remote past or in another country, medical records may not be obtainable. In such cases, it is encouraging to note that an extremely large study found a 1% uterine rupture rate despite the fact that 90% of the trial of labor patients had unknown uterine scars.⁸ If prior medical records are not available, it is helpful to ask the patient why she had her initial cesarean operation. In the majority of cases, the patient will describe dystocia or failure to progress, conditions rarely associated with either classical or low vertical uterine incisions. However, if the operative report is not available and the patient gives a history consistent with premature breech, transverse lie, or placenta previa, elective repeat cesarean may be prudent.

Can Uterine Rupture Be Predicted?

Several groups have attempted to predict uterine rupture by ultrasound evaluation of the uterine scar prior to or during early labor. In theory, the thickness of the previous scar could be measured and a “critical value” could be determined that would predict uterine rupture. In practice, this has not worked out. Thinning of the lower uterine segment is a normal part of labor, and measurements taken 2 hours apart may show great variation. Additionally, measurement of minuscule differences in soft tissue thickness (1 or 2 mm) may not be reproducible. The previous scar may not be detectable on ultrasound examination. Even on direct examination and palpation at the time of repeat cesarean, it is often difficult to observe the previous uterine incision. Thus, at this time there is no reliable method for predicting uterine rupture.

Detection of Uterine Rupture

Older literature described “classical” warning signs of uterine rupture, including maternal hypotension, maternal tachycardia, excessive vaginal bleeding, and hematuria. Although any of these signs may occasionally occur with uterine rupture, they are not reliable and may be late indicators. “Atypical” abdominal pain or “pain over the previous incision” were also commonly mentioned in the older literature as indications of uterine rupture, but it is extremely difficult to evaluate abdominal pain in the midst of active labor. One study reported that in 95% of emergency repeat cesarean operations performed because of severe abdominal pain felt to be indicative of uterine rupture, no rupture was found.¹³ Because pain is an unreliable indicator of uterine rupture, there is no evidence that epidural anesthesia will mask a warning sign. Many large studies have concluded that it is reasonable to use epidural anesthesia in patients attempting VBAC. It had also been hoped that the intrauterine pressure catheter (IUPC) would be helpful in the diagnosis of uterine rupture. In theory, uterine rupture would be immediately indicated by loss of the contraction pattern. However, two studies have shown the IUPC to be unreliable in the detection of uterine rupture. Fetal heart rate monitoring appears to offer the best hope for early diagnosis of uterine rupture. Prolonged deceleration of the fetal heart rate (often termed bradycardia) or repetitive severe variable decelerations may be the first indication of uterine rupture.¹⁴ Prolonged decelerations can certainly occur in the absence of uterine rupture and frequently occur in patients with no uterine scar. Nevertheless, when a prolonged deceleration occurs during a trial of labor and does not recover within several min-utes, uterine rupture must be suspected.

Predicting Success of Vaginal Birth After Cesarean

The patient who is pondering VBAC will frequently ask her obstetrician to estimate her chance for a vaginal birth. She may believe that her body is abnormal and that she is physically unable to deliver without surgery. In fact, such anatomic abnormalities are quite uncommon. Most studies have found the success rate for VBAC to be approximately 75% when patients with all indications for primary cesarean are included. Thus, the likelihood of vaginal birth for a woman attempting VBAC is similar to that of a nulliparous patient with no prior cesarean. A meta-analysis of 29 studies found that VBAC success rates ranged from 67% for patients with prior failure to progress in labor to 85% for patients with a prior cesarean for breech presentation.¹⁵ The authors concluded that there appeared to be no variables studied for which success rates were so low that trial of labor would constitute inappropriate patient care. More recently, attempts have been made to develop VBAC scoring systems to predict VBAC success rates.¹⁶ These systems are helpful in identifying the 5% of patients at each end of the spectrum who are very likely to succeed or very likely to fail. Unfortunately, these systems are not very predictive for the remaining 90% of VBAC candidates. Additionally, those patients most likely to fail a trial of labor (e.g. the patient with a prior cesarean for failure to progress who has had no prior vaginal birth and who is now postdates with an unfavorable cervix) can be predicted without the aid of any scoring system.

How Does Prenatal Care Differ From That of a Patient With No Prior Cesarean?

Attempts to ascertain the type of previous uterine incision should begin early in the course prenatal care. If a prior classical uterine incision is confirmed, it is prudent to schedule the patient for elective repeat cesarean as soon as American College of Obstetrics and Gynecology (ACOG) criteria are met and to warn her to call immediately if she begins to have contractions. This is because a classical uterine incision, unlike the common low transverse incision, has a propensity to rupture before the onset of labor. Patients without contraindications to trial of labor should be informed of their options and offered their choice of VBAC or elective repeat cesarean. In many cities, the International Childbirth Education Association (ICEA) and/or American Society for Psychoprophylaxis in Obstetrics (ASPO/Lamaze) offer VBAC classes in which the risks versus benefits of these two options are discussed in detail. If placenta previa is identified in a patient with one or more prior cesarean sections, the obstetrician should be aware of the possibility of placenta previa accreta. Finally, prenatal care of the patient with a prior cesarean delivery includes informed consent issues.

What Constitutes Informed Consent for Vaginal Birth After Cesarean?

The topic of informed consent for VBAC remains controversial. At issue is exactly how much information must be imparted to constitute truly informed consent. If doctors discussed every potential problem that could develop during any pregnancy, many women would never have children. Such a misguided attempt at risk management would strike needless fear into the hearts of the millions of women who experience uncomplicated pregnancies each year. Textbooks and journals are filled with accounts of horrible complications that, fortunately, occur very rarely. The goal of informed consent is to present clinically significant risks, benefits, and alternatives in an understandable and unbiased fashion. In the case of VBAC (assuming the primary uterine scar was not classical), the patient should understand that the risks of pregnancy and labor are almost identical to those faced by a patient with no prior cesarean. The one exception is the increased risk of uterine rupture. Patients considering VBAC should be informed that in about 1 of 100 cases the uterus will rupture during a trial of labor. They should also be informed that if the uterus does rupture, there is a significant risk to mother and baby. Finally, a truly informed consent must clearly point out that the alternative to VBAC, planned repeat cesarean, is not risk-free.

Must VBAC Consent Be Written?

In the early 1980s elective repeat cesarean was still routine at many U.S. hospitals, and VBAC was uncommon. At that time, written VBAC consent forms were commonly used for those women who opted to attempt VBAC. By the early 1990s, VBAC had become so commonplace that most doctors no longer used written VBAC consent forms. However, an article published in 1996 strongly advocated the use of written VBAC consent forms, and that recommendation has gained widespread acceptance.¹⁷ In the unusual case of a bad outcome, the written consent will document the fact that the patient was fully informed regarding the risks versus benefits of both alternatives and that she was offered a choice of either VBAC or elective repeat cesarean. A sample consent form is shown in Figure 1.

Cervical Ripening Agents and Vaginal Birth After Cesarean

A large multicenter study of prostaglandin gel for cervical ripening in patients with prior cesarean found no increased risk of uterine rupture.¹⁸ A review of the literature reported similarly favorable results.¹⁹ However, other studies have linked rupture of the scarred uterus to cervical ripening agents.²⁰ In light of this possibility, and because studies on outpatient cervical ripening have not included VBAC patients, it would seem prudent to avoid outpatient cervical ripening in the patient with a scarred uterus.

Oxytocin and Vaginal Birth After Cesarean

Several studies have found no significant increase in the rate of uterine rupture when oxytocin is used during a trial of labor.²¹ A meta-analysis of 31 studies reached the same conclusion.²² Nevertheless, oxytocin has been associated with uterine rupture, even in patients with no uterine scar. Thus, it would seem prudent to exercise caution when inducing or augmenting a patient with a scarred uterus.

Vaginal Birth After Cesarean With Prior Single-Layer Closure

Most of the large VBAC studies involved patients who had two-layer closure of the uterine wall during their primary cesarean. In the 1990s, single-layer closure of the uterus became quite popular, and there was some concern that the incidence of uterine rupture during subsequent trial of labor might rise. However, there is no documented evidence that single-layer closure results in a weaker scar than two-layer closure. Although there is not yet much data on the subject, preliminary studies indicate that there is no increased risk of uterine rupture in patients who have had single-layer closure.²³

Trial of Labor With More Than One Prior Cesarean

Most studies have concluded that trial of labor with two prior low transverse cesareans is a reasonable option. A large study found the risk of uterine rupture to be 1.8% with two prior cesareans versus 0.6% with one prior cesarean.⁷ Data on outcomes of trial of labor in patients with more than two prior cesareans is limited, but the risk of rupture appears to be similar to that of patients with two prior cesareans.

Vaginal Birth After Cesarean in the Patient With Obstetric Complications

In the pregnancy complicated by factors such as twins, breech, suspected fetal macrosomia, and postdates, the patient's motivation for vaginal birth is paramount. In any of these situations, if the patient has little interest in VBAC, elective repeat cesarean would seem prudent. However, if the patient strongly desires vaginal birth, trial of labor is not contraindicated by any of these factors. More than 100 cases of VBAC with twin gestation have been reported in the medical literature, and although the numbers are small, the reports indicate that trial of labor is a reasonable option for highly motivated patients. For the patient with breech presentation and a prior low transverse cesarean, external cephalic version appears to be a reasonable option. Theoretical concerns about rupture of the previous scar during a version attempt have not been substantiated in practice.²⁴ As with VBAC of twins, the number of version patients studied thus far is small, and therefore the results must be interpreted with caution. Suspected fetal macrosomia is not a contraindication to attempted VBAC in the nondiabetic patient. A study comparing 301 trials of labor with actual birth weights greater than 4000 g to 1475 trials of labor with actual birth weights less than 4000 g found no increase in uterine rupture or morbidity in the group with larger infants.²⁵ As would be expected, the vaginal birth rate was significantly lower (55% versus 78%) in the group with larger infants. The patient who opts for trial of labor but reaches 42 weeks' gestation without the onset of spontaneous labor presents a dilemma. Although induction of labor is a reasonable option, the patient may wish to rethink her options if the cervix is unfavorable.

What if the Patient Changes Her Mind About Vaginal Birth After Cesarean?

ACOG guidelines indicate that, after being informed of the alternatives, the option of trial of labor (for appropriate candidates) or elective repeat cesarean is the patient's choice.²⁶ It seems to follow that if a patient initially opts for trial of labor but later changes her mind and requests elective cesarean delivery, her decision should be honored. The converse would also be true. However, once the patient is in labor, the situation is not as clear. Patients frequently request or demand cesarean section in the midst of labor; yet, appropriately, obstetricians generally do not perform a cesarean operation unless there is a valid medical indication for surgery. It would be quite unusual to perform a primary cesarean on patient in early labor just because she wanted one. More typically, the patient would be offered pain relief and labor support and would very likely go on to deliver vaginally without complications. However, there is no consensus on how to respond to the VBAC patient who requests cesarean section during labor.²⁷ One reasonable option would be to initially offer the same labor support and pain relief measures that would be offered to any laboring patient. If, despite these measures, the patient still wishes to abandon her trial of labor, it would seem wise to perform a repeat operation.

Strategies for Making Vaginal Birth After Cesarean Safer

Hundreds of studies have reached the conclusion that VBAC is a relatively safe option. Nevertheless, it is well-documented that uterine rupture occurs in about 1% of VBAC attempts. Being cautious with oxytocin and cervical ripening agents may lower this number slightly but will not solve the problem. Huge multicenter studies indicate that the approximately 1% incidence of uterine rupture is an unavoidable component of VBAC.^3,5,7 There is also currently no method of predicting which patients are most likely to sustain a uterine rupture. Thus, efforts to make VBAC safer hinge on improving outcomes when the inevitable uterine rupture does occur. This, in turn, seems to rely on rapid detection and rapid intervention. The most recent ACOG guidelines for VBAC make this clear when they state, “Because uterine rupture may be catastrophic, VBAC should be attempted in institutions equipped to respond to emergencies with physicians readily available to provide emergency care.”²⁶ The message seems clear, but the definition of “readily available” is open to interpretation. In some communities it is not possible to have obstetricians and anesthesiologists in the hospital 24 hours per day. For example, in a community with only two obstetricians, this would mean perpetual every-other-night in-house call—clearly an untenable situation. However, there are potential alternatives. An obstetrician and anesthesiologist may choose to remain in the hospital or at an office very close to the hospital on those few nights when they have a VBAC patient in labor. If this is not feasible, it may be reasonable to refer those patients who want a trial of labor to centers that do have 24-hour in-house obstetric and anesthesia services. Another way to make not only VBAC but all labors safer is to practice “crash” cesarean drills with the goal of moving a patient to the operating room and having her ready for surgery in the shortest possible time. Finally, a “crash” cesarean tray, including only those instruments needed to delivery the baby, will avoid wasting time while searching for and counting instruments.

The editor of a major medical journal recently concluded that rising VBAC rates and the resultant elimination of the need for more than 100,000 repeat cesarean operations each year in the United States alone has been the greatest single change in obstetric practice in the past generation. It has become clear that the VBAC option is here to stay. However, it must be emphasized that neither VBAC nor its alternative, planned repeat cesarean delivery, are risk-free. The only way to eliminate the risks associated with each of these two options is to obviate the need for both of them. This can only be accomplished by avoiding the primary cesarean that permanently scars the uterine wall. In some cases (e.g. transverse lie, placenta previa, abruption) the need for primary cesarean is absolutely clear. In other cases, such as unfavorable cervix or “slow labor,” the issue is much more cloudy. In these borderline cases, it must be remembered that the uncomplicated primary cesarean done today may become the complicated repeat cesarean, lethal placenta previa accreta, or catastrophic uterine rupture of tomorrow.

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