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UK Study finds men also have biological clock: Conception takes longer for older men

1 August 2000

The older a man is, the longer it is likely to take his partner to conceive irrespective of her age, according to research published today.

The older a man is, the longer it is likely to take his partner to conceive irrespective of her age, according to research published today (Tuesday 1 August) in Human Reproduction*.

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 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 and for conception within 12 months decrease by 3% every year.

A decline in male fecundity (the likelihood of achieving a pregnancy within a define period of time) has never before been confirmed or quantified by studies in the general population, so this research by teams at Bristol and Brunel universities** is the first to provide clear evidence that the age of the man, as well as the woman, is an important factor in conception.

The conclusions have been drawn from data provided by the Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC), known locally as the Children of the 90s, which was designed to evaluate the effects of personal, social and environmental factors on the development of children from early pregnancy onwards. It had involved 85% of the pregnancies of couples living in the Avon Health Authority 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 Bristol and Brunel teams used these data to evaluate the effect of men’s age on the time taken to achieve pregnancy.

Kate North, researcher in the Children of the 90s study, said: “It is really difficult to quantify the effect of men’s age on fecundity because it is confounded 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 to be ultimately 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.

“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,” said Dr Chris Ford of the University Division of Obstetrics and Gynaecology at St Michael’s Hospital, Bristol.


*W.C.L Ford et al.  Increasing paternal age is associated with delayed conception in a large population of fertile couples: evidence for declining fecundity in older men. Human Reproduction. Vol. 15. No. 8. pp1703-1708. doi: 10.1093/humrep/15.8.1703

**Division of Obstetrics and Gynecology and Division of Paediatric and Perinatal Epidemiology, University of Bristol; Brunel University Department of Health Studies.



1. Full embargoed text of the paper with participating research teams can be found from 0.900 BST (date to be entered) on website:

2. Human Reproduction is a monthly journal of the European Society of Human Reproduction and Embryology. Please acknowledge Human Reproduction as a source.

3. Printed text available on request from Dr Helen Beard, Managing Editor.

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