Progesterone may not lower risk of repeated miscarriage

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Pregnant women who have had several miscarriages in the past are sometimes given progesterone supplements, in hopes of avoiding another miscarriage. But a new study shows these hormone supplements do not increase the chances of maintaining the pregnancy in these women.

In the study, researchers found no difference in birth rates between women who received progesterone treatments during their first trimester of pregnancy and those who received a placebo at that time. Among the women given the supplements, 65.8 percent maintained their pregnancy, compared to 63.3 percent of those given the placebo. The researchers took into account the women's age, ethnicity, medical history and pregnancy history.

"That 2.5 percent is an extremely tiny difference, and is not statistically significant," said Dr. Arri Coomarasamy, a researcher at the University of Birmingham in England and the lead author on the new study. In other words, the difference could have been due to pure chance.

During the study, 826 women between ages 18 and 39 who had previously had unexplained, recurrent miscarriages and who were actively trying to conceive were randomly selected to use a daily vaginal supplement of either 400 milligrams of progesterone, or a placebo, up until week 12 of their pregnancy, according to the study published Nov. 25 in The New England Journal of Medicine. [6 Myths About Miscarriage]

Progesterone is essential for achieving and maintaining a healthy pregnancy. The hormone is made by a structure within the ovary called the corpus luteum, as well as by the placenta during pregnancy, Coomarasamy said.

"Based on previous studies, we had hoped that progesterone would help to increase the likelihood of [having] a baby for women with a history of recurrent miscarriage," Coomarasamy told Live Science. "Our findings are bound to come as a disappointment to many thousands of women and couples affected by this condition."

Some previous research has suggested that progesterone supplementation during the first trimester of pregnancy could lower the risk of recurrent miscarriages. A 2014 study looked at the use of an oral form of progesterone called dydrogesterone up until week 20 of pregnancy. The study results revealed that the miscarriage rate was 2.4 times higher in the placebo group than in the women who received the hormone — suggesting that progesterone treatments could be extended for longer periods.

A number of earlier studies that were smaller and less-rigorously controlled also reported benefits of progesterone supplementation during the first trimester of pregnancy, Coomarasamy said. However, he added, a 2013 comprehensive review study concluded that many of those studies were poorly designed, and the researchers called for further research to investigate the question.

While the new findings may seem disappointing, Coomarasamy says that a lot can be learned in the future about women taking progesterone for other reasons, such as fertility treatments.

"We will continue to explore and test other treatments," Coomarasamy said. Ongoing studies include the PRISM trial, which is testing whether progesterone could reduce the risk of miscarriage in women with bleeding during early pregnancy, and the TABLET trial, which is testing whether a drug called levothyroxine could reduce the risk of miscarriage in women with certain thyroid problems.