Natural progesterone could help women who have suffered two or more unexplained miscarriages to have a successful pregnancy, according to a study published in the journal Fertility & Sterility.

Around 25% of pregnant women suffer a miscarriage during the first trimester of pregnancy. For some women, unexplained miscarriages occur repeatedly with each of their pregnancies.

To help these women have successful pregnancies, researchers at the University of Illinois at Chicago, USA studied the effect of administering micronized natural progesterone two days prior to ovulation on a group of 116 patients who had previously suffered two or more unexplained miscarriages.

Natural progesterone is a so-called "bio-identical" hormone with the same molecular structure progesterone produced by the ovaries. "Traditional" synthetic hormones, on the other hand, present certain chemical differences.

Progesterone plays an essential role in preparing the uterus for egg implantation and then maintaining gestation.

The scientists found that natural progesterone, administered vaginally, led to a higher birth rate in the women studied. In fact, over two thirds of pregnancies were successful in women who received the treatment, compared to less than half for those who didn't.

The study suggests that analyzing endometrial health in cases of repeated pregnancy loss could prove useful. It is possible to detect abnormal endometrial development by examining the expression of a molecular marker called nCyclinE. In the future, this kind of test could be used to establish which women could benefit from progesterone treatments and at what dose.

A further clinical trial is required to validate the study's encouraging initial findings.

The study is published in Fertility & Sterility, the international journal of the American Society for Reproductive Medicine.