Risk of Miscarriage May Not Be Lowered By Progesterone

Pregnant women who have recurrent miscarriages are sometimes prescribed progesterone supplements to avoid future miscarriages, but it seems as though these supplements do not help women maintain their pregnancy, according to a new study.

In the study – published November 25 in The New England Journal of Medicine – the researchers found no significant difference in birth rate between women who received progesterone during their first semester of pregnancy and those who were given a placebo.

About 65.8 percent of the women who received the progesterone supplements maintained their pregnancy, compared with approximately 63.3 percent of the women who received the placebo. That small difference may have occurred due to chance, the researchers say.

Dr. Arri Coomarasamy, lead author on the new study and a researcher at the University of Birmingham in England, said that the 2.5 percent is a very small difference which makes the study not statistically significant.

For the study, the researchers selected a number of 836 women ages 18 to 39 who have had several miscarriages in the past and who were actively trying to conceive, and gave them either a daily supplement that had 400 milligrams of progesterone, or just a placebo. The study was conducted over a twelve-week period. The women’s age, medical history, ethnicity, and pregnancy history were also taken into account.

Progesterone is vital for maintaining a healthy pregnancy. The hormone is made in the ovaries by the corpus luteum (“yellow body”) – a temporary endocrine structure in female mammals. During pregnancy, progesterone is also produced in increasingly high amounts by the placenta, according to Dr. Coomarasamy.

Previous studies suggested that progesterone supplements during the first trimester of a woman’s pregnancy might decrease the risk of miscarriage.

In a 2014 study, the researchers analysed the use of oral progesterone supplements called dydrogesterone. They observed the effects of dydrogesterone for up to 20 weeks into the pregnancy. The final results showed that for the women in the placebo group the miscarriage rate was 2.4 times higher, compared with women who were given the progesterone supplements.

Although there were a number of previous less-rigorously controlled studies which found that progesterone supplements are beneficial especially in the first trimester of pregnancy, a 2013 review study disproved all the results, saying that those studies were poorly constructed.

Dr. Coomarasamy said that they will continue to test other treatments. Currently there are two ongoing studies: the TABLET trial, which tests whether levothyroxine can decrease the risk of miscarriage in pregnant women who have thyroid problems, and the PRISM trial, which tests whether progesterone can reduce the risk of miscarriage in women who tend to bleed early into pregnancy.

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