Women who are thought to have a macrosomic fetus may be encouraged to attempt VBAC, if they so desire. Macrosomia is a minor risk factor for failure of a trial of labor, but it does not necessarily increase the risk of uterine rupture.15
Elkousy examined VBAC success rates by birth weight, indication for the previous cesarean delivery, and pregnancy history. Not surprisingly, increased birth weight or a history of cephalopelvic disproportion reduced the rate of success, but a history of vaginal delivery negated that risk of failure. A history of successful VBAC improved the chance of success to more than 90%—even when the birth weight exceeded 4,000 g—and the success rate reached 82% when the birth weight exceeded 4,500 g.16
Does VBAC have a future?
Physician and hospital attitudes toward vaginal birth after cesarean delivery (VBAC) may be a major determinant of its frequency and success. Many forces oppose women who desire a trial of labor after cesarean. Hospitals and insurers make it increasingly difficult to offer a trial of labor, and strict interpretation of ACOG’s guidelines requiring personnel to be “immediately available” during a trial of labor has caused many smaller and isolated hospitals to stop offering this option. The number of women who attempt VBAC has plummeted.20
Two recent surveys by ACOG indicate that an alarming number of providers have stopped offering VBAC because of a lack of insurance and fear of legal liability. As providers offer a trial of labor less and less, skills decline, and so does mentorship of younger physicians.
The NIH weighs in
In March 2010, the National Institutes of Health (NIH) convened a consensus development conference on the topic of VBAC. A panel of health professionals and public representatives reviewed the medical literature and produced a consensus statement. Their conclusion:
- Given the available evidence, [a trial of labor] is a reasonable option for many pregnant women with a prior low transverse uterine incision. The data reviewed in this report show that both [a trial of labor] and elective repeat cesarean for a pregnant woman with a prior transverse uterine incision have important risks and benefits and that these risks and benefits differ for the woman and her fetus.
The panel’s goal was to help women who have a history of cesarean delivery make an informed, evidence-based decision about the subsequent mode of delivery. The panel also acknowledged the general lack of high-quality evidence to confidently quantify the risks and benefits of a trial of labor versus planned repeat cesarean delivery.21
For another point of view on vaginal birth after cesarean, see the Editorial, “Does vaginal birth after cesarean have a future?” by John T. Repke, MD, of the OBG Management Board of Editors.
Repeat cesarean is probably best for obese gravidas
Obesity increases the likelihood of cesarean delivery in all circumstances, so it is not surprising that it is a risk factor for a failed trial of labor after cesarean. Obesity also increases the risks of anesthesia and surgery. Because of these risks, most clinicians opt to deliver obese patients by scheduled elective cesarean rather than risk having to perform emergent cesarean delivery in the case of acute fetal compromise or uterine rupture.
Race is not a risk factor for rupture
Race is probably not a significant independent risk factor for failure of VBAC. A secondary analysis of a multicenter, retrospective, cohort study found that black women were somewhat more likely to fail a trial of labor than white women (OR, 1.50; 95% CI, 1.29–1.74), after adjustment for confounding variables. However, black women undergoing a trial of labor were 40% less likely to suffer a uterine rupture than white women were.17
When comorbidities are well managed, VBAC remains an option
In general, a trial of labor in women who have well managed chronic medical disease does not pose undue risk to mother or baby.
In a population-based, retrospective cohort study using discharge data from California, Gregory and coworkers attempted to delineate clinical variables that might be associated with VBAC success and complications. They examined a wide range of maternal conditions, from diabetes to chorioamnionitis, as well as fetal conditions, such as oligohydramnios and unengaged vertex. Mothers were stratified into low- and high-risk groups, and multivariate logistic regression was performed. Low-risk patients had a 73.7% success rate, whereas high-risk patients had a 50% success rate. Not surprisingly, women who had a fetus with an unengaged vertex had a 9.8% chance of success and an eightfold increase in the risk of uterine rupture.18