Progesterone supplements fail to improve birth rate among women with a history of miscarriage

By Sally Robertson, B.Sc.Nov 26 2015

A new study has shown that taking progesterone supplements during the first trimester of pregnancy does not improve the chances of maintaining pregnancy among women who have a history of unexplained recurrent miscarriage.

Previous studies have suggested that supplementation with progesterone, which is essential for achieving and maintaining pregnancy, may lower the risk of miscarriage among such women. However the current findings mark the end of a five-year trial, finally providing an answer to decades of uncertainty over the matter.

As reported in the New England Journal of Medicine, Arri Coomarasamy (University of Birmingham, England) and colleagues selected 826 women (aged 18 to 39 years) with a history of unexplained recurrent miscarriages who were actively trying to conceive. The women were given a daily vaginal supplement of either 400mg progesterone or a placebo to use for the first 12 weeks of pregnancy.

The researchers report that there was no significant difference in pregnancy rate between those who used progesterone and those who did not. This was true after taking into account the women’s age, ethnicity, medical history and pregnancy history.

Of the women who received the hormone supplement, 65.8% maintained their pregnancy and gave birth to their baby, compared with 63.3% of those who received the placebo.

"That 2.5 percent is an extremely tiny difference, and is not statistically significant,” says Coomarasamy, meaning the difference could easily have been a result of pure chance.

Although the finding will be disappointing to many, it does answer a question that people have been asking since progesterone was first suggested as a treatment back in 1953. It will allow researchers to direct their efforts elsewhere and explore other potential therapies.

“It may well be that progesterone supplements have other uses, such as preventing miscarriage in women with early pregnancy bleeding, so it’s not the end of the road.”

Arri Coomarasamy.

At the moment, ongoing studies include the PRISM trial, which is looking at whether progesterone can reduce miscarriage risk among women with bleeding during early pregnancy and the TABLET trial, which is testing whether a drug called levothyroxine can reduce miscarriage risk in women with certain types of thyroid disorder.