Progesterone prevents preterm birth in women with short cervix, ineffective in those with twins

Progesterone is effective in preventing premature birth in women with a short cervix but ineffective in preventing premature birth in women pregnant with twins, according to two studies in the Aug. 2 issue of the New England Journal of Medicine.

In the first study, Kypros H. Nicolaides, MD, from King's College Hospital Medical School in London, and colleagues randomly assigned 413 pregnant women with a cervix less than 15 mm long to 200 mg vaginal progesterone per night or placebo from 24 to 34 weeks' gestation. They found that progesterone significantly reduced the risk of spontaneous delivery before 34 weeks (RR, 0.56) and tended to reduce the risk of neonatal morbidity (RR, 0.59).

In the second study, Dwight J. Rouse, MD, from the University of Alabama in Birmingham, and colleagues randomly assigned 665 women pregnant with twins to intramuscular injections with 17 alpha-hydroxyprogesterone caproate or placebo starting at 16 to 20 weeks' gestation to 35 weeks. They found that the risk of delivery or fetal death before 35 weeks and the risk of serious adverse neonatal events were similar in both groups (RR, 1.1 for both).

Fonseca EB, Celik E, Parra M, et al. Progesterone and the risk of preterm birth among women with a short cervix. N Engl J Med. 2007;357:462-469.

Rouse DJ, Caritis SN, Peaceman AM, et al. A trial of 17 alpha-hydroxyprogesterone caproate to prevent prematurity in twins. N Engl J Med. 2007;357:454-461.