Progesterone is a sex hormone that is essential for the maintenance of pregnancy. However, taking progesterone supplements during the first 12 weeks of pregnancy does little to help women with a history of unexplained, recurrent miscarriages.

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The trial found that taking progesterone in the first trimester did not help women with unexplained, recurrent miscarriages avoid another loss.

This was the conclusion of a 5-year trial led by the University of Birmingham in the UK and published in the New England Journal of Medicine.

The findings of the PROMISE (progesterone in miscarriage treatment) trial – conducted in 45 hospitals in the UK and the Netherlands – settle 60 years of uncertainty about whether progesterone is an effective treatment for preventing miscarriage in women with a history of unexplained, recurrent losses.

The randomized, double-blind, placebo-controlled trial included 826 women of average age 33 years with previously unexplained recurrent miscarriage. They received twice-daily vaginal suppositories of either progesterone or matched placebo for up to 12 weeks of gestation.

After analyzing the results, the authors conclude that:

“Progesterone therapy in the first trimester of pregnancy did not result in a significantly higher rate of live births among women with a history of unexplained recurrent miscarriages.”

This was true regardless of age, ethnicity, medical history and pregnancy history, they note.

Nearly two thirds of the participants carried to full term and had their babies, with no significant difference between the treatment group (65.8% live birth rate) and the placebo group (63.3% live birth rate).

Lead author Arri Coomarasamy, a professor in Birmingham’s College of Medical and Dental Sciences, says while the results are disappointing, “there are a number of other positives that we can take from the trial as a whole.”

By finally settling the decades-long question, the study allows researchers to direct their efforts toward exploring other treatments that can reduce the risk of miscarriage.

The trial found no significant negative effects of taking progesterone in pregnancy – either for the women or their babies. This is reassuring for women taking progesterone for other reasons – because they are having fertility treatment, for example, or taking part in other trials.

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

He says another positive thing to come out of the trial is the strong network of health professionals now established in the UK and beyond that is committed to miscarriage research, and notes:

That wealth of expertise and information will be invaluable as we continue to explore and test other treatments that really can reduce the risk of miscarriage.”

Earlier this year, Medical News Today learned of a survey that found there is widespread misperception about miscarriages among Americans. For instance, 1 in 5 people surveyed said they believed lifestyle choices such as smoking and substance abuse during pregnancy were the primary causes of miscarriage, when 60% are actually caused by chromosomal abnormalities.