Progesterone for the prevention of preterm birth among women at increased risk: a systematic review and meta-analysis of randomized controlled trials.

OBJECTIVE: This study was undertaken to determine whether progestational agents, initiated in the second trimester of pregnancy, reduce the risk of delivery less than 37 weeks, among women at increased risk of spontaneous preterm birth. STUDY DESIGN: Medline, pre-Medline, EMBASE, and Cochrane Central Register of Controlled Trials were searched. Randomized controlled trials with less than 20% lost to follow-up were included. RESULTS: Three trials were eligible for inclusion. There was a significant reduction in risk of delivery less than 37 weeks with progestational agents (relative risk [95% CI] = 0.57 [0.36-0.90]). There was no significant effect on perinatal mortality or serious neonatal morbidity. CONCLUSION: Progestational agents, initiated in the second trimester of pregnancy, may reduce the risk of delivery less than 37 weeks' gestation, among women at increased risk of spontaneous preterm birth, but the effect on neonatal outcome is uncertain. Larger randomized controlled trials are required to determine whether this treatment reduces perinatal mortality or serious neonatal morbidity.