What's Wrong with This Picture?
The study authors defined "trial of labor" as any vaginal birth or emergency cesarean after 37 weeks of pregnancy.
This means that any woman who had a uterine rupture (scar gives way) or placental abruption (placenta separates prematurely from the uterus) during pregnancy and presented at the hospital requiring emergency cesarean would be classified as a "trial of labor." The mortality in such cases would be high because these life-threatening events would occur outside of the hospital. The odds of uterine rupture in pregnancy in a woman with a uterine scar are 2 per 1,000, and the odds of placental abruption are 3 per 1,000 (11). Of course, not every baby would die, and many cases would occur earlier than 37 weeks. Still, do the math on the 15,500 so-called trials of labor, and you will see that several, if not many, of the 20 infant deaths in the "trial of labor" group weren't really trials of labor.
With one exception, the study didn't evaluate the effects of obstetric management. The researchers looked at the effect of inducing labor with prostaglandin E2 (Cervidil, Prepidil) and found no association; however, two other studies have reported strong associations (8,12). Several studies suggest that oxytocin (Pitocin) used to induce labor or possibly even to stimulate stronger contractions poses some increased risk and should be used sparingly in VBAC labors (2,3,13). The study reports that 15 percent of the trial-of-labor group was induced with prostaglandin E2 but does not say what percentage had oxytocin inductions or augmentations. Note: Misoprostol (Cytotec) induction, a potent cause of uterine rupture, doesn't appear to be an issue here (5).