Progesterone effects on preterm birth in high-risk pregnancies: a randomized placebo-controlled trial.

Purpose: The purpose of this study was to evaluate whether the prophylactic administration of vaginal progesterone would reduce the preterm birth rate in high-risk population including singleton and twin pregnancies.

Methods: This was a randomized, double blind, placebo-controlled study that included 150 high-risk pregnancies. Risk groups included prior spontaneous preterm birth, twin pregnancy, and uterine malformation. Micronized progesterone or placebo (100 mg) was administered daily by vaginal suppository between 24 and 34 weeks of gestation. We compared progesterone and placebo groups for incidence of preterm labor and preterm delivery. Data were compared by χ² analysis and Fisher exact test.

Results: There was a statistically significant difference in the rate of preterm labor between placebo and progesterone groups (45.7 vs. 25%, respectively; p < 0.05). More women delivered before 37 weeks in placebo group (57.2%) than in progesterone group (40%; p < 0.05). Administering progesterone also reduced the preterm birth before 34 weeks of gestation. The difference between placebo and progesterone group was statistically significant (24.3 vs. 8.8%; p < 0.05). However, there was no significant difference in neonatal death between placebo and progesterone groups.

Conclusion: Prophylactic vaginal progesterone reduced the rate of preterm labor and preterm delivery in high-risk pregnancies.