Progesterone has been used in the treatment of women with unexplained recurrent miscarriages for years, but experts have had varying opinions about its efficacy. A new study conducted by researchers from the University of Birmingham shows that progesterone does not help improve the condition of women with a history of miscarriages.

In the five-year trial called progesterone in miscarriage treatment (PROMISE), the researchers recruited 826 women who have had previous unexplained miscarriages to determine if treatment with progesterone would make them less likely to miscarry. They were given 400 mg of micronized progesterone twice daily within the first trimester of pregnancy. The research also included a placebo group.

The rate of live birth for the treatment group was 65.8 percent, while that for the placebo group was 63.3 percent. The researchers concluded that the treatment did not make the women less prone to miscarriage regardless of their age, medical and pregnancy history and ethnicity.

The results of the study, according to the authors, ends the long-standing debate about the efficacy of progesterone in improving pregnancy outcomes for women who have had repeated miscarriages.

"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," study author Arri Coomarasamy said in a press release. "Fortunately, there are a number of other positives that we can take from the trial as a whole."

One of these positives is that progesterone treatment was found to have no negative effect in both the mothers and the babies, indicating that it is safe for those it as a treatment for fertility purposes. Additionally, Coomarasamy said that progesterone treatment can be used for the prevention of bleeding during the early stages of pregnancy.

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

The study was published online Nov. 26 in The New England Journal of Medicine.