Scientists have discovered why some women may be prone to recurrent miscarriages.

The team from the UK has pinpointed molecular signals in the body, which appear to control whether embryos are accepted by the womb. These signals seem to function abnormally in women who have suffered miscarriages repeatedly.

It has long been known that a fertilised embryo must become embedded in the lining of the womb for a pregnancy to successfully proceed. This is known as implantation. Furthermore, the womb is only receptive to this happening on a few days each month. However, little is known beyond this.

The scientists looked at the molecular signals produced by cells taken from the lining of the womb, which were subsequently grown in a laboratory. They found that one particular molecule - IL-33 - appeared to play a key role in the implantation process.

According to the team, the effects of molecular signals in the womb do not last long, ensuring that a woman can only conceive on specific days during her menstrual cycle. However, the scientists found that women with high levels of the IL-33 signal continued to have it released for up to 10 days later. This indicated that the womb's ability to accept an embryo was not functioning correctly.

In further studies involving IL-33 and mice, the scientists found that these signals extended the time the animals could become pregnant, but they warned that this increased the risk of an abnormal embryo implanting in the womb, increasing the risk of a miscarriage.

"Our study suggests that in women who have had successive miscarriages, the mechanisms that control whether the womb can accept and support an embryo don't work properly. This might mean they can become pregnant with poor quality embryos or that the embryo implants in an unsupportive environment, which would seriously compromise the chances of a successful pregnancy," explained one of the scientists, Dr Madhur Salker, of Imperial College London.

The team suggested that drugs which target these molecular signals could help prevent miscarriages in certain women.

Details of these findings are published in the journal, PLOS ONE.