International Federation of Gynecology and Obstetrics

The female body has an in-built system which rejects sperm that it does not think will create a pregnancy, researchers have found.

Within the female reproductive system there is something that assesses to see whether the male's sperm is likely to fertilise the eggs, resulting in a pregnancy, reports ABC News.

"Some combinations of men and women might not be compatible and it's possible that the immune systems of some women aren't responding correctly to their partner's triggering molecules," the news provider quoted lead researcher Professor Sarah Robertson of the University of Adelaide as saying.

So far, the tests have been carried out on mice and pigs but Professor Robertson believes the study would produce similar results on human females.

"We've discovered that there are signalling molecules in the seminal fluid, so that after coitus when that fluid travels from the male to the female reproductive tissues it activates gene expression changes and also changes in the female immune system that increase the likelihood of a pregnancy occurring," she said.

According to the most recent data from the Office for National Statistics, the UK fertility rate was 1.96 children per woman in 2008, which is the highest level since 1973.

Posted by Martine Ward