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Am Fam Physician. 2003;67(5):931-936

Vaginal birth after cesarean delivery (VBAC) appears to go in and out of fashion. Enthusiasm for VBAC peaked in 1996, when 28.3 percent of women with previous cesarean delivery underwent trial of labor, and declined to 16.5 percent in 2001.1,2 Growing concerns about uterine rupture and the attendant risk of infant perinatal mortality were key factors in the shift away from VBAC and the call for more repeat cesarean deliveries.3

In a 1999 practice bulletin, the American College of Obstetricians and Gynecologists (ACOG) recommended the following: “Because uterine rupture may be catastrophic, VBAC should be attempted in institutions equipped to respond to emergencies with physicians immediately available to provide emergency care.”4(p5) The evidence for this recommendation was described as level C (based primarily on consensus and expert opinion). The ACOG later commented that the definition of “immediately available” was left for each hospital to decide, although the title of the comment was “Cesarean Delivery Resources Need To Be Available During VBAC Trial of Labor.”5

The ACOG recommendation has caused significant disruption for patients and physicians who are interested in VBAC. Obstetricians and family physicians are troubled by the implications of the recommendation.6 Because of these implications, some hospitals are no longer offering VBAC services.7

A comprehensive analysis of the literature by the American Academy of Family Physicians (AAFP)8 found that in most women with previous cesarean delivery, trial of labor was safe and preferred to elective repeat cesarean birth. The AAFP concluded, however, that women should be able to choose between the delivery methods, because outcomes were similar and some women preferred cesarean birth.9 Subsequent larger studies have shown that with trial of labor, rates of uterine rupture and associated infant perinatal mortality are higher than previously believed (Table 1).8,1013

Source of dataSymptomatic uterine rupture (per 10,000)Perinatal deaths (per 10,000)
AAFP (1995)8: meta-analysis of 292 studies2410
McMahon, et al. (1996)10: 6,138 patients2740
Mozurkewich and Hutton (2000)11: 47,682 patients4020
Lydon-Rochelle, et al. (2001)12: 15,515 patients52 (spontaneous labor) 77 (induced; no prostaglandins)NA
Smith, et al. (2002)13: 313,238 patientsNA12

No randomized trials have compared trial of labor and elective repeat cesarean birth. Large population-based studies have shown no difference in maternal mortality between the two delivery approaches. Compared with trial of labor, elective repeat cesarean birth is associated with a 2 percent greater risk of maternal infection10,14 and a 1 percent greater risk of maternal hemorrhage requiring transfusion.15 Uterine rupture occurs 0.24 to 0.77 percent more frequently with trial of labor than with repeat cesarean birth,8,12 and perinatal death occurs 0.10 to 0.40 percent more frequently.8,10 All of the above percentages reflect absolute, not relative, differences. For infant perinatal morbidity, no meaningful comparisons can be made because studies have not collected data in a manner that permits conclusions.

While the data outlined above constitute the current state of knowledge, the attitudes and values attached to possible outcomes are also important. A woman with previous cesarean delivery must balance the slightly higher risks of uterine rupture and infant perinatal mortality associated with trial of labor against the modestly higher risks of maternal infection and hemorrhage associated with elective repeat cesarean birth. Other considerations include the woman's views about the experience of vaginal birth, the predictable scheduling of elective repeat cesarean delivery, and the financial implications of the method of delivery.9 Of course, the woman's preferences may become irrelevant if she does not have access to VBAC services.

The irony of the ACOG recommendation is that it may result in what it seeks to avoid: worse pregnancy outcomes and increased litigation risk. As more maternity services are discontinued and women must leave their communities for pregnancy care, mortality and morbidity rates increase for both mothers and infants.16 Furthermore, in most locations, it is not possible to assure every woman undergoing trial of labor that she will have cesarean resources “immediately available” at all times in her labor. Even if a surgeon could be in the hospital at all times, other women in the birthing unit may need cesarean resources at the same moment. As a result, there will likely be legal battles over what “immediately available” really means. Finally, even in units where cesarean resources are available at all times, evidence suggests that the time from decision to delivery is seldom less than 30 minutes, maternal injury increases with rushed cesarean delivery, and infant acidosis and severe morbidity and death are not prevented.1720

Meanwhile, patients and physicians are faced with difficult choices about trial of labor and elective repeat cesarean birth. Patient selection factors that may increase the chance for successful VBAC are listed in Table 2.4,12,2130 A strategy of shared decision-making is best: the patient and physician must talk about risks and options.

The reason for the original cesarean delivery is not present this time (e.g., breech presentation last time, cephalic presentation this time).4
There is no cephalopelvic disproportion.21
Labor begins spontaneously, and the cervix is dilated 3 to 4 cm on initial evaluation.22
Induction is not used,23,24 particularly prostaglandin induction.12,25
Augmentation is not used.12,24
Instrumental delivery (vacuum or forceps) is not used.26
Fetal weight is estimated to be less than 4,000 g (8 lb, 12 oz).27
More than 6 months have elapsed between the last delivery and this pregnancy.28
The woman has had one previous normal vaginal delivery.29
The woman has already had one successful VBAC.26
The woman has had one low transverse cesarean delivery.4
The woman is still motivated to try labor after thinking through the possibility of an unsuccessful trial of labor (i.e., a long labor and a repeat cesarean delivery).30
The woman understands the risks associated with trial of labor and elective repeat cesarean birth. The risk of uterine rupture can be described as a 0.5% chance that it will happen or a 99.5% chance that it will not happen; data should be presented in as many ways as the patient requires to make an informed decision (see Table 1).

Use of a consent form has been suggested. This form would ask any woman who is considering VBAC to acknowledge the following: “If my uterus ruptures during my VBAC, there may not be sufficient time to operate and to prevent the death of my baby or permanent brain injury to my baby.”31(p68),32 However, this form does not provide immunity against a law suit, because the infant who experiences adverse outcomes was not party to the consent process and has legal rights. Therefore, the consent form has been described as something “no one in their right mind would sign.”33(p661) Instead, informed choice should be revisited every time there is a significant change in preference or circumstance. If, for example, a woman requests a repeat cesarean delivery during a lengthy trial of labor, her request should be respected.

Uterine rupture is an uncommon but highly serious event. Repeat cesarean delivery is not a risk-free proposition either. Given the lack of reliable predictors about which VBAC candidates are likely to experience uterine rupture, the best that physicians can do is to engage patients in continuous conversation, throughout pregnancy and labor, about the status, risks, and options for the pregnancy and delivery method.

Physicians must remain vigilant for the cardinal sign of uterine rupture (significant fetal heart rate deceleration that is progressive and severe) and must be ready to effect cesarean delivery as rapidly as possible within parameters determined locally. The latter requires careful coordination and communication among all members of the maternity care team.

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