Quantifying VBAC risk: muddying the waters.

The Landon et al and the Crowther et al papers are both prospective trials comparing planned vaginal birth after a previous cesarean section (VBAC) with elective cesarean section in women eligible for a trial of labor. With 33,000 women, the cohort studied by Landon et al in conjunction with the National Institute of Child Health and Human Development (NICHHD) spawned multiple publications, giving estimates of VBAC risks and success relevant to women in a wide variety of clinical situations. Data abstraction was careful and outcomes were hard and verified. With 2,300 women, the study by Crowther et al, was 6 percent the size of the Landon-NICHHD study. Although it claimed "increased risk of both fetal death or liveborn infant death prior to discharge or serious infant outcome," there were only 2 perinatal deaths-both stillbirths prior to 39 weeks' gestation and unrelated to mode of delivery. Of the 28 infants with "serious neonatal morbidity," only three could have resulted from uterine rupture; prior experience with this outcome indicates all three will likely escape long-term morbidity. Pseudorandomization and erroneous adherence to an intention-to-treat principle seriously hinder the study's internal validity, attributing outcomes for one quarter of women undergoing elective cesarean section to the planned VBAC group. The study by Landon and NICHHD is over 10 times larger and of much higher quality than the study by Crowther et al. The Landon-NICHHD publications should be used to help women make decisions about planned mode of delivery after cesarean.