Background: In 2007, nearly one third of all U.S. births were by cesarean delivery, the highest proportion ever recorded. The most common indication for cesarean delivery is previous cesarean birth. There has been a substantial decline in the rates of vaginal birth after cesarean (VBAC) delivery, falling from a high of 28.3 percent in 1996 to only 8.7 percent in 2007. There was a corresponding increase in the proportion of women who chose an elective repeat cesarean delivery over a trial of labor. The effects of these trends on maternal and neonatal health outcomes are unclear. Guise and colleagues systematically reviewed the evidence on factors associated with successful VBAC delivery, and the benefits and harms to the mother and infant from a trial of labor.

The Study: Multiple electronic databases were searched for English-language publications through September 2009 that addressed one or more relevant topics. From 3,134 abstracts retrieved in initial searches, 203 articles were included in the review. Studies were conducted in the United States and other developed countries and reported maternal or perinatal outcomes of a trial of labor (resulting in VBAC or repeat cesarean delivery). Studies of women with other indications for repeat cesarean delivery (e.g., breech position) and studies of preterm deliveries (i.e., delivery before 37 weeks of gestation) were excluded. Perinatal death was defined as death occurring before 28 days of age or at 20 weeks of gestation or later.

Results: Based on 43 observational U.S. studies, 74 percent of women who have a trial of labor after a previous cesarean birth deliver vaginally; this proportion has remained constant over time despite the decline in VBAC delivery rates. Factors associated with successful VBAC delivery include a history of vaginal birth, normal birth weight, white race, and tertiary care center setting (as opposed to a rural or community hospital). There was insufficient evidence to determine the effect of oxytocin (Pitocin) augmentation or epidural analgesia on VBAC delivery rates.

The risk of uterine rupture was statistically higher in women undergoing a trial of labor (0.47 percent) compared with women undergoing an elective repeat cesarean delivery (0.026 percent). Fourteen to 33 percent of women who experienced a uterine rupture underwent a hysterectomy. Maternal mortality was rare, but higher in women undergoing an elective repeat cesarean delivery (13.4 deaths per 100,000 deliveries) than in those undergoing a trial of labor (3.8 per 100,000). In contrast, trial of labor was associated with higher perinatal mortality (1.3 deaths per 1,000 deliveries) than elective repeat cesarean delivery (0.5 per 1,000). Most studies found no differences in neonatal intensive care unit admission rates. Few studies examined differences in breastfeeding initiation, respiratory distress, or neonatal trauma.

Conclusion: The authors conclude that, compared with elective repeat cesarean delivery, VBAC delivery appears to be a reasonable and safe choice for most women. The evidence suggests that most of the differences in maternal and perinatal outcomes between these delivery options are statistically, but not clinically, significant.

editor's note: Since 1996, about one third of hospitals and one half of physicians providing maternity care have stopped offering trials of labor to women with previous cesarean delivery because of concerns about uterine rupture and medicolegal issues.¹ A National Institutes of Health panel that considered evidence reviewed by Guise and colleagues has called on the American Congress of Obstetricians and Gynecologists and the American Society of Anesthesiologists to reconsider VBAC delivery guidelines requiring that surgeons and anesthetists be “immediately available” to respond to complications from a trial of labor. Notably, an independent panel convened in 2005 by the American Academy of Family Physicians found no evidence to support this requirement.²—k.l.