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Tuesday, 1 August, 2000, 08:08 GMT 09:08 UK
Men 'have a biological clock'
Older men's sperm may not be so good at fertilisation
The older a man is, the longer it is likely to take his partner to conceive - irrespective of her age, researchers have found.

The odds on conceiving in up to six months of trying decrease by 2% for every year that the man is over the age of 24, according to a study published in Human Reproduction.

The chances of conception within 12 months decrease by 3% for every year.

Men as well as women have a biological clock that starts ticking as they get into their thirties

Dr Chris Ford, St Michael's Hospital, Bristol

In addition, women whose partners are five or more years older than themselves have less chance of conceiving in under a year of trying than women whose partners are the same age, or younger.

The research, by scientists from Bristol and Brunel Universities, is the first to confirm that the age of a man is an important factor in conception.

The findings are based on an analysis of data generated by a long-term study into pregnancy and childhood.

The research, being carried out in the Avon area, is known as the Children of the 90s study. It is designed to evaluate the effects of personal, social and environmental factors on the development of children from early pregnancy onwards.

It focuses on 85% of the pregnancies of couples living in the Avon Health Authority area whose babies were due between 1 April 1991 and 31 December 1992.

Over 8,500 of the couples who said their pregnancies were planned had stated the time taken to conceive.

The researchers used the data to evaluate the effect of men's age on the time taken to achieve pregnancy.

Complex subject

Professor Ian Craft
Professor Ian Craft said lifestyle could also be a factor

Researcher Kate North said: "It is really difficult to quantify the effect of men's age on fecundity because it is compounded by so many factors.

"But after adjusting carefully for all the variables we still found that women with older partners were significantly less likely than women with younger partners to conceive in under six or 12 months.

"Because of the size and composition of the study we are confident that our findings are robust and that the effect is real."

The study concluded that in a couple who prove ultimately to be fertile, the probability that it will take more than 12 months to conceive nearly doubles from around 8% when the man is under 25 to around 15% when he is over 35.

Dr Chris Ford, of the University Division of Obstetrics and Gynaecology at St Michael's Hospital, Bristol, said: "It tells us that to some degree men as well as women have a biological clock that starts ticking as they get into their thirties and it also indicates that paternal age is another factor to be taken into account when doctors are looking at the prognosis for infertile couples."

Professor Ian Craft, director of the London Fertility Clinic, said the impact of male fecundity had not been extensively researched.

"We assume that men have the same fertilisation capacity from the time they become fertile, to the time they die, but that is probably not the case, in fact it is odd to think that men do not experience some deterioration in their sperm quality with time."

Professor Craft said it was likely that the number of sperm containing chromosomal abnormalities increased over time.

There was also a possibility that lifestyle factors, such as smoking, had some impact.

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See also:

11 Jul 00 | Background Briefings
The future of fertility
18 Mar 00 | Health
Absence 'boosts sperm levels'
28 Feb 00 | Health
Sperm boost may aid fertility
02 Jan 00 | Health
Hope for infertile men
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