Clinical Question: Do progestational agents started in the second trimester of pregnancy prevent preterm birth for women at increased risk?

Setting: Various

Study Design: Meta-analysis (randomized controlled trials)

Synopsis: The meta-analysis included three randomized placebo-controlled trials with 648 women in which progestational agents were started in the second trimester to prevent preterm birth. Studies that did not present data according to intention to treat and those with more than 20 percent of participants lost to follow-up were excluded. Two studies used weekly intramuscular progesterone injections (250-mg 17-alpha hydroxyprogesterone caproate). The other study used natural progesterone administered in 100-mg intravaginal suppositories daily. The risk of preterm delivery was significantly lower with treatment (relative risk = 0.57; 95% confidence interval, 0.36 to 0.90; number needed to treat = 6). The risk of a less than 2,500-g birth weight was similarly reduced. However, the meta-analysis failed to identify any differences in perinatal mortality or serious morbidity.

Bottom Line: Second-trimester progestational agents significantly reduce the risk of birth before 37 weeks’ gestation in women at increased risk of preterm birth. Reduction in perinatal mortality or serious morbidity has not yet been established. Additional, larger trials are needed. (Level of Evidence: 1a–)