Dr. Knight and her colleagues used an intention-to-treat analysis that looked at the primary outcome as a risk ratio, with a 95% CI. Secondary outcomes, also presented as risk ratios, were considered with a 99% CI.
A total of 3,427 women were randomized. In all, 1,715 women in the active arm and 1,705 in the placebo arm were included in the outcomes analyses. Women were interviewed by telephone, they completed questionnaires, and they received a questionnaire by mail or completed one online. Slightly more than 1,500 women in each arm completed the phone interview, and nearly 1,300 in each arm completed the initial questionnaire.
The mean age was 30 years, and most of the participants (84%-87%) were white. Most were of normal weight, with a median body mass index at the initial prenatal visit of 25 kg/m2.
Though women with multiple pregnancies were included in the study, just 11 in the active arm and 9 in the placebo arm delivered twins. There were no triplets. Most women (76%-78%) were primiparous, and just 7%-8% of women had prior cesarean delivery.
The mode of operative delivery for most of the participants (63%-67%) was forceps, with all but 10 of the remaining women receiving vacuum extraction (the remaining 10 had spontaneous vaginal deliveries).
The reasons for instrumental delivery were approximately evenly divided between failure of labor to progress and fetal compromise.