Progesterone Prevents Preterm Birth for Some Women

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For this study, British researchers measured the cervical length of nearly 25,000 pregnant women. They found 413 (1.7 percent) had a short cervix. From that group, they randomized 250 of the women to receive either 200 milligrams of vaginal progesterone, administered nightly, or a placebo.

In this population, researchers found a significant benefit from the progesterone therapy. Delivery before 34 weeks of gestation occurred in 19.2 percent of those receiving progesterone vs. 34.4 percent of those on placebo.

"This study certainly gives hope to women diagnosed with short cervix," said Welch, who added that progesterone is a fairly inexpensive treatment, generally costing less than $100 for therapy throughout pregnancy. And, he said, it appears to be safe to use in pregnancy.

As to why one study showed a benefit while the other didn't, Thorp said it's likely that there are likely numerous pathways or mechanisms that lead to preterm birth, and there will likely have to be numerous therapies to prevent each type of preterm birth. It could also be that one study used injectable progesterone, while the other was administered vaginally, or it might be that twins or triplets need higher doses of progesterone.

"There are a lot of things we try to prevent preterm birth, but few are effective. In women with a history of preterm delivery, preliminary studies have shown progesterone can reduce preterm birth and there are no birth defects associated with it. We don't have anything else to offer women with a history of preterm birth. And we haven't had really had anything to offer women with a short cervix up to this point. Unfortunately, it looks like with twins, we still don't have a lot to offer," Welch said.

More information

To learn more about preterm labor and birth, visit the March of Dimes.