Can Progesterone Prevent Preterm Birth?

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Can Progesterone Prevent Preterm Birth?

Progesterone shows promise, but it’s uncertain when it is most beneficial.

Progesterone is necessary to maintain pregnancy, in part because it inhibits uterine contractility. Studies in some animal models indicate that progesterone levels fall markedly before onset of labor, and 17 alpha-hydroxyprogesterone acetate (17P) has been shown to reduce the rate of recurrent preterm birth (Journal Watch Jun 24 2003). Two new multisite randomized double-blind trials address the efficacy of progesterone in women at increased risk for preterm labor.

In the first study, 655 women with twin gestations received weekly intramuscular injections of 17P or placebo beginning at 16 to 20 weeks of gestation and ending at 35 weeks. Delivery or fetal death before 35 weeks was not significantly different in the two groups.

In the second study, 413 women with cervical length of 15 mm or less on transvaginal sonography examination at 20 and 25 weeks of gestation received either vaginal progesterone or placebo from 24 to 34 weeks of gestation. Significantly fewer women in the progesterone group than in the placebo group had a spontaneous birth before 34 weeks (19.2% vs. 34.4%; relative risk, 0.56). However, no significant difference was observed in neonatal morbidity.

Comment: We still do not have definitive answers about the utility of progestogens for preventing preterm labor. Further studies are clearly needed to clarify when progestogens may be beneficial, especially because preterm birth is the leading cause of neonatal morbidity and mortality in the U.S. A review article in the same issue summarizes the wide range of known contributing factors that underlie the causes of preterm labor.

— Robert W. Rebar, MD

Published in Journal Watch General Medicine August 1, 2007