Keep on trying - when you do get pregnant the chances are it will be a boy!

A team of Dutch researchers at Maastricht University say that women who take longer to get pregnant are more likely to give birth to a boy.

The Dutch researchers looked at 5,283 women who gave birth between July 2001 and July 2003.

The team say they found that women whose cervical mucus is relatively thick have more problems conceiving naturally because of the difficulties faced by the sperm.

They found that male sperms were better able to cope with the thicker mucus.

Apparently around 58 per cent of women who had tried to conceive naturally for over a year had a boy, compared to 51 per cent who became pregnant in a shorter time.

The researchers calculated that each year of trying gave couples a 4 per cent higher chance of having a boy.

This was the case even when taking into account factors such as age, smoking and alcohol use.

They suggest one explanation could be that male sperm is more successful at implanting in the womb.

Despite the fact that the proportions of X (female) and Y (male) sperms in human semen are equal, more boys than girls are born around the world in a ratio of 105 to 100.

The researchers said their findings support the theory that Y chromosome sperms are able to swim faster than X chromosome sperms in thick, viscous fluids.

If couples did manage to conceive naturally, after a longer time of trying, they were more likely to conceive a boy because the Y sperms were better able to cope with the thicker mucus.

The team say that they did not find a link between the sex of babies and time taken to get pregnant in couples who received medical help to conceive.

The report is published in the British Medical Journal.