Study: Men Have a Biological Clock
Emma Ross,
AP Medical Writer

7:46 PM EDT; July 31, 2000; London, UK (AP) -- Once a man passes the age of 24, the older he is, the longer it takes for him to make his partner pregnant, regardless of her age, a new study suggests. A decline in male fecundity -- the likelihood of achieving pregnancy within a certain period of time -- has never before been confirmed or quantified in the general population, experts say. The research, published Tuesday in the European Journal Human Reproduction, provides the first clear evidence that the age of a man, as well as that of a woman, could be an important factor.

"It tells us that, to some degree, men as well as women have a biological clock that starts ticking as they get into their 30s," said Dr. Chris Ford of St. Michael's Hospital of Bristol, England, who led the study. "It also indicates that paternal age is another factor to be taken into account when doctors are looking at the prognosis for infertile couples," Ford said. The study examined whether men become less fecund as they get older, as opposed to less fertile.

Fertility refers to the ability to produce a baby, while fecundity refers to the ability to do it within a certain period of time. If it takes a man 20 years to make his partner pregnant, he is fertile but not very fecund. "Fecundity is a critical thing because, as the female ages, her ability to conceive declines dramatically. And if the man is not fecund, by the time he can impregnate his partner, it is too late because she is too old," said Dr. Christopher Barratt, a British fertility expert who was not connected to the study. The research involved 8,500 British couples whose pregnancies were planned and successful. It found that the probability it would take more than a year to conceive nearly doubled from about 8 percent when the man was under 25 to about 15 percent when he was over 35. The chance of a man making a woman pregnant within a year of trying decreased by three percent for every year he was over the age of 24. The chance of impregnating a woman within six months declined by two percent for each year he was over 24.

"It shows what we've suspected for a long time, and it all makes scientific sense," Barratt said. "The evidence of declining male fertility has been based on indirect measures -- cutting up the testes and seeing the number and quality of sperm. This is direct evidence."

But another expert was more cautious about the findings. Dr. Berhard Nieschlang, Director of the Institute of Reproductive Medicine at the University of Muenster in Germany, said the study may have underestimated the importance of the man's age because it excluded couples who had miscarriages and those who failed to conceive at all. Miscarriages are more commonly linked to older men, he said. On the other hand, he said, it may have overestimated the effect by not accounting well enough for the fact that some men -- usually younger ones -- have more sex and thus more opportunities to make their partners pregnant. "But it's on a large scale and ... it's an important observation," Nieschlang said of the study. "So far, the notion was only that female fertility declines, and there has been no proof that men's declines too." Experts agreed it is difficult to determine the importance of a man's age because it is hard to disentangle that factor from the numerous others that influence conception. The study involved a diverse group of people, and the results were adjusted in an attempt to eliminate the influence of such factors as alcohol, existing children, contraceptive pill use, smoking, education, and the woman's age. Barratt said he was convinced the effect was real, even if the study did not eliminate the influence of the frequency of intercourse. He said that, "in general, having sex more than twice a week does not increase the probability of conception."