Master Class

Increasing the Odds for Success With VBAC

Vaginal birth after cesarean gained widespread acceptance in the 1980s after a National Institutes of Health Consensus Development Conference panel questioned the necessity of routine repeat cesarean deliveries and described situations in which a VBAC should be offered. Some insurers even mandated that physicians attempt a VBAC prior to a repeat cesarean delivery.

Since 1996, however, the VBAC rate has dropped substantially while cesarean delivery rates have risen steadily. The overall cesarean delivery rate was approximately 32% when last measured in 2007, up from 21% in 1996. The VBAC rate was less than 10% in 2007, compared with 28% in 1996, according to the Centers for Disease Control and Prevention.

Indeed, pregnant women now have limited access to VBAC services, and many are not even offered the option of having a trial of labor after cesarean. Some hospitals have declined to provide VBAC services, and the most recent medical liability survey conducted by the American College of Obstetricians and Gynecologists showed that almost 20% of responding fellows stopped offering or performing VBACs between 2006 and 2008. (In the prior survey, completed in 2006, these numbers were even higher—upward of 26%.)

The exact causes of the decline in VBAC deliveries are unclear, but the shift likely involves a mix of concerns about the possibility of uterine rupture, patient preferences, medicolegal pressures, guidelines that call for the immediate availability of personnel to perform an emergency cesarean, and other clinical and nonclinical factors.

It is a complex and concerning trend—one considered important enough to the health of women in the United States for the NIH to recently convene another Consensus Development Conference panel on the topic. The panel was asked to examine the causes of VBAC decline as well as the available research on the benefits and harms of attempting a trial of labor after a patient has had a cesarean delivery.

In a draft statement titled, “Vaginal Birth After Cesarean: New Insights,” released in March, the panel affirmed that a trial of labor is a reasonable option for many women with a prior cesarean delivery. It also urged that current VBAC guidelines be reconsidered and more research conducted.

Although guidelines are being revisited and research ensues, we owe it to the patients in our own practices to thoroughly consider what is known about the short- and long-term safety of VBAC, the selection of candidates, and the most reasonable approaches to intrapartum management.

Short-Term Safety of VBAC

In the past decade, there have been two large observational studies in the United States that have shed much light on the efficacy and safety of a trial of labor after cesarean. Both studies involved upwards of 20,000 women, and both showed rates of uterine rupture under 1%. This finding is significant, because some have suggested that uterine rupture is on the rise in the United States.

In one of these studies—a prospective cohort study conducted from 1999 through 2002 at 19 academic medical centers belonging to the National Institute of Child Health and Human Development Maternal-Fetal Medicine Units (MFMU) Network—there were 124 cases of uterine rupture among 17,898 women who underwent a trial of labor after cesarean, and no cases of uterine rupture among 15,801 women who underwent elective repeat cesarean delivery.

The rate of uterine rupture was 0.7% for women with a prior low transverse incision, 2.0% for those with a prior low vertical incision, and 0.5% for those with an unknown type of prior incision. Overall, the rate of uterine rupture in this study was 0.7% (N. Engl. J. Med. 2004;351:2581-9).

The second study, which I led, revealed a rate of uterine rupture in women who attempted VBAC of 0.9%, compared with a rate of 0.004% in women who underwent elective repeat cesarean section. This study was a multicenter observational study in which records of approximately 25,000 women with a prior low-transverse cesarean section were reviewed (Am. J. Obstet. Gynecol. 2005;193:1656-62).

Just as uterine rupture is more common in women who have a VBAC attempt than in those who choose elective repeat cesarean section, so are adverse perinatal outcomes. The MFMU study found 12 cases of hypoxic ischemic encephalopathy (HIE) among the term infants whose mothers underwent trials of labor. Seven of the cases of HIE were associated with uterine rupture.

Perspective is important. Although uterine rupture and HIE—the complications of most concern—are higher among those who attempt VBAC, the absolute rates are quite low and are comparable to, if not lower than, the complication rates of most other obstetrical procedures we perform on a daily basis.


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