New research finds that progesterone supplements in the first trimester of pregnancy do not improve outcomes in women with a history of unexplained recurrent miscarriages.

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. The findings 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.

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 of the University of Birmingham explains, "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.