Time waits for no man's sperm, new study finds

The biological clock ticks for men as well as women, suggesting it is not just females who should be aware of the consequences of starting families later in life, according to research published yesterday.

In the biggest ever study into the effects of paternal age on babies' health, scientists found that older men have a greater chance of fathering children with Down's syndrome and are more likely to have babies with limb defects.

Previous have found that sperm, as well as eggs, accumulate genetic mutations as they age, which can lead to a drop in male fertility. But the effect of such genetic damage on children born to older fathers has proved hard to pin down.

In the latest study, epidemiologist Jorn Olsen, at the University of California, Los Angeles, used the Danish Fertility Database, which holds information on 70,000 couples and their firstborn child, to look for differences in children with older fathers. Men aged 50 and above were more than four times more likely to have a child with Down's syndrome. Children with limb defects were also more common.

The study appears in the journal Human Reproduction.

The finding caused concern in the UK on Wednesday among some fertility specialists, who have seen the age of sperm donors increase with the UK's abolition of sperm donor anonymity earlier this year.

"With the change in the law, donors tend to be men who have already had their families," said Allan Pacey, a fertility expert at Sheffield University, England.

"But about a third of all births in the UK are from men who are older than 35 and, frankly, that's not the best sperm to use in fertility treatment," Pacey said.