Men have biological clocks too

A man's fertility starts to decline from the age of 24, according to a new study carried out by researchers based at the UK's Bristol and Brunel Universities. The scientists found that the older a man is, the longer it will take his partner to conceive, regardless of her age. They estimate that the chances of conceiving within six months decrease by two per cent for every year that the man is over 24. Their results are published in the journal Human Reproduction.

The teams used data from the Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC), which was set up to investigate the factors affecting the health and development of thousands of babies born in the area between April 1991 and December 1992. 'It is the first study that demonstrates there is a real decline in fertility as men get older' said Dr Chris Ford, one of the team leaders. He added that paternal age should be another factor to take into account when doctors were looking at treatment options for infertile couples.

Dr Ford said the possible reasons for falling male fertility included reduced production of the hormone testosterone, and environmental factors such as pollution affecting sperm quality. But he stressed that although fertility in both sexes declines with age, 'there is still an 85 per cent chance on average of a couple in their mid-thirties conceiving within a year'.