Vaginal Progesterone for Preventing Preterm Birth May Not Live Up to Its Promise

Since 2003, progestins have been favored for preventing preterm birth: Efficacy seemed clear in studies that included high-risk women, although progestin formulations (intramuscular or vaginal) varied from trial to trial. To determine the longer-term benefits and harms of vaginal progesterone, investigators in the U.K. conducted a multicenter trial of this agent in 1228 women with specified combinations of risk factors. Participants were randomized to self-administered vaginal progesterone (200 mg daily) or placebo from 22 to 34 weeks' gestation.

Women in the progesterone group were no less likely to experience adverse obstetric or neonatal events (including delivery at <34 weeks) than women in the placebo group. Outcomes in offspring at age…