WIRED-UP women students will soon be sniffing men's T-shirts as part of a bizarre but serious study into fertility problems.

Researchers at Newcastle University have recruited half of the 160 young women needed for a study which could raise serious questions about possible side-effects of oral contraceptives.

Women will be asked to sniff T-shirts worn by six different men and rate them according to attractiveness.

During the experiment, the women will be wired-up to electronic monitors which will trace physiological reactions.

The experiment will be repeated a few months after the same women have gone on the Pill.

Another group of women, who are trying to get pregnant, will be asked to take part to compare results.

The North-East experiment follows up studies involving mice, which suggest that females instinctively choose mates which have a dissimilar genetic make-up.

This seems to make conception easier and increases the chances that any offspring will be healthy.

But a small-scale study in Switzerland which involved humans suggests that this instinct may be being masked by the effects of being on the Pill.

Pregnant women, or those on the Pill, tended to chose more genetically similar mates.

The theory is that pregnant women, or those whose bodies are mimicking pregnancy, are attracted to those who smell similar to their own kind.

Scientists are suspicious that this spin-off from the Pill could account for increasing infertility problems in modern society.

Craig Roberts, a behavioural ecologist, said: "There is a suggestion that the Pill is altering women's preferences for genetically dissimilar men, which may be a matter for concern."

Because the Swiss study was so small the Newcastle team has decided to carry out a larger-scale experiment.