A potential cause of miscarriages has been identified by scientists - a breakthrough that could lead to the development of new drugs that prevent them.

Laboratory tests showed women who had lost three or more babies had high levels of a molecule known as IL-33 in their womb cells.

In the future. medicine to target the protein could be given to pregnant women who are particularly vulnerable.

Tests found that women who had suffered successive miscarriages had high levels of a certain molecule in their womb cells

The researchers said the molecule controls whether embryos are accepted by the womb.

But women who had suffered multiple miscarriages continued to secrete it for an extra ten days, they found.

The receptivity of the womb was not being controlled properly in these women, according to the findings published in the journal PLOS ONE.

Dr Madhuri Salker, of Imperial College London, said: 'Our study suggests 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 the embryo implants in an unsupportive environment, which would seriously compromise the chances of a successful pregnancy.'

Healthy embryo: A prolonged window of fertility increases the risk of abnormal embryos implanting

The study also looked at the effects of these molecular signals on fertility in mice.

The researchers treated the uteruses of the mice with chemicals secreted by cells from the human womb lining.

They found chemicals produced by cells from women with repeated miscarriages extended the time during which mice could become pregnant, but also made miscarriages more likely.

The researchers conclude a prolonged window of fertility increases the risk of abnormal embryos implanting.

In addition, it is associated with inflammation in the lining of the womb, which compromises the development of healthy embryos.

Study co-author Professor Jan Brosens, of the University of Warwick, said: 'The molecular signals we identified are known to be involved in a range of diseases including Alzheimer's, asthma and heart disease.

'Our findings suggest targeting these molecules might also be a promising strategy for developing treatments that would prevent miscarriages in women who are especially vulnerable.'

At the start of pregnancy, the fertilised embryo must embed itself in the lining of the womb which is only receptive for a few days in each menstrual cycle, ensuring they can only implant at the right stage of development.

Currently, scientists know only a few details about the biological processes that control when an embryo can be implanted.