New research from the University of Birmingham has shown that progesterone supplements in the first trimester of pregnancy do not improve outcomes in women with a history of unexplained recurrent miscarriages.

The findings, published today in The New England Journal of Medicine, mark the end of a five year trial and provide a definitive answer to 60 years of uncertainty on the use of progesterone treatment for women with unexplained recurrent losses.

The study of 826 women with previously unexplained recurrent miscarriage showed that those who received progesterone treatment in early pregnancy were no less likely to miscarry than those who received a placebo. This was true whatever their age, ethnicity, medical history and pregnancy history.

Nearly two thirds of the women in the trial had their baby, whether they had progesterone or the placebo. The live birth rate was 65.8% in the treatment group, and 63.3% in the placebo group.

Though the results of the PROMISE (progesterone in miscarriage treatment) trial will be disappointing to many, it will allow researchers to direct their efforts towards exploring other treatments that can reduce the risk.

Professor Arri Coomarasamy explained, “We had hoped, like many people, that this research would confirm progesterone as an effective treatment.  Though disappointing, it does address a question that has remained unanswered since progesterone was first proposed as a treatment back in 1953. Fortunately, there are a number of other positives that we can take from the trial as a whole.”

The trial results also showed that there were no significant negative effects of progesterone treatment for women or for their babies.  This is important information for women taking progesterone for other reasons, such as fertility treatment, or for those taking part in other trials.

Professor Coomarasamy continued, “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.”

“Furthermore, the PROMISE trial created a solid network of doctors, nurses and midwives across the UK and beyond, all committed to miscarriage research. 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.”

Read more about the Tommy's National Centre for Miscarriage Research

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PROMISE was a randomised, double-blind, placebo-controlled trial, conducted across 36 hospital sites in the UK and nine in the Netherlands.

Women could enrol in the study if they were 18-39 years old, and actively trying to conceive naturally after being diagnosed with unexplained recurrent first trimester miscarriage.  They were also excluded from the study if they did not conceive within 12 months of being enrolled.

• 1,568 eligible women were signed up to take part in the trial.  Of these
• 732 did not start the trial at all for a number of reasons (515 because they did not conceive within 12 months) and another ten either started and then stopped or were lost to follow-up.  That left:
• 826 women who completed the trial and were followed all the way through.  Of these:
• 398 women were in the treatment group and 428 were in the placebo group.
• Their average age was 33.