VBAC: When is it safe?
When do risks outweigh benefits, in light of ACOG’s newly cautious advisory? What conditions call for extra concern?
In the same study, the relative risk of uterine rupture was 3.3 for women presenting in spontaneous labor, compared with those who underwent repeat cesarean without labor; it was 15.6 and 4.9 for women whose labor was induced with prostaglandins or by other means, respectively. The rate of infant mortality was 5.5% in cases involving uterine rupture, compared with 0.5% without rupture.25
Note that this study covered the years 1987 through 1996—and thus predated ACOG rules requiring round-the-clock obstetric and anesthesia care, and those barring prostaglandins for labor induction.
Perinatal death more likely with VBAC, but absolute risk is low
A separate population-based, retrospective, cohort study18 focused on different outcomes: intrapartum stillbirth or neonatal death. This study involved 313,238 singleton births at 37 to 43 weeks’ gestation with the fetus in a cephalic presentation.
Among the women opting for VBAC, the overall rate of delivery-related perinatal death was 12.9 per 10,000 women. This was approximately 11 times greater than the risk associated with planned repeat cesarean, more than twice the risk associated with labor in multiparous women, and similar to the risk among nulliparous women in labor. However, in absolute terms, the risk of perinatal death associated with a trial of labor and uterine rupture was low: 1 in 2,200.18
What’s the bottom line?
Are findings such as these reason to abandon VBAC? Not necessarily. VBAC success rates range from 60% to 80%, and a 1991 meta-analysis43 of more than 30 US studies found lower maternal febrile morbidity after a trial of labor than after repeat cesarean, and no differences between the 2 approaches in uterine dehiscence, rupture, or perinatal mortality.
A more recent meta-analysis9 of international studies involving 47,682 women found a uterine rupture rate of 0.4% for women undergoing a trial of labor versus 0.2% for those having elective repeat cesarean. A later meta-analysis, also international, found an overall uterine rupture rate of 6.2 per 1,000 women attempting VBAC, with a perinatal mortality rate of 0.4 per 1,000. Perinatal mortality was significantly lower among US studies.6
Nevertheless, when it comes to VBAC, absolute risks are low, and planned repeat cesarean does not eliminate them entirely. Elective cesarean carries a risk of maternal death up to 2.8 times that of vaginal delivery, though absolute risk is low.44
Thus, when patients are carefully selected and fully informed of benefits and risks, VBAC should remain an available option.
The author reports no relevant financial relationships.
