MEN have a biological clock which starts to tick when they turn 40, a new study suggests.
Infertility specialists found that miscarriage rates increased significantly and pregnancy rates dropped when the father was older than 40.
It is the first time paternal age has been seen to have such a strong effect on reproductive success.
A
lthough the study involved thousands of men and women being treated for infertility, its findings are relevant to all couples, the researchers said.
Dr Stephanie Belloc, the study leader from the Eylau Centre for Assisted Reproduction in Paris, said: "Until now, gynaecologists only focused on maternal age and the message was to get pregnant before the age of 35 or 38.
"But now the gynaecologists must also focus on paternal age and give this information to the couple."
Dr Belloc's team followed up a total of 21,239 artificial insemination procedures carried out between January 2002 and December 2006.
The 12,236 couples had decided to try intrauterine insemination (IUI) after having difficulty conceiving. IUI involves spinning sperm in a centrifuge to separate it from seminal fluid and then inserting it directly into the womb.
Before each procedure, researchers noted the quantity, activity and shape of the man's sperm. Pregnancy, miscarriage and delivery rates were also recorded. Detailed analysis allowed the scientists to separate male and female factors relating to pregnancy success or failure.
As expected, the pregnancy rate was significantly reduced for women over the age of 35 while the miscarriage rate was higher. But the study unexpectedly found that being older than 40 also made it harder for men to become fathers.
For men aged under 39 the miscarriage rate was 16.7 per cent. But after the age of 40 it rose sharply to about 35 per cent.
Pregnancy rates also only began to change significantly when men reached 40.
As men's age increased from 39 to 44 the proportion of treatment cycles producing a pregnancy fell from 13.4 per cent to 10.9 per cent.
Professor Yves Menezo, who worked on the study, said: "We found the paternal impact on miscarriage was much stronger when men passed age 40."
He added: "As expected, older women were less likely to get pregnant and had more miscarriages than younger ones, but surprisingly the risk of miscarriage was also far higher for couples in which the man was past 40, about 35 per cent."
The findings were presented at the weekend at the meeting of the European Society of Human Reproduction and Embryology in Barcelona, Spain.
Many reports show an overall decline in sperm count and quality as men age, but experts have disagreed on whether or not this is simply the result of getting older. Lifestyle factors such as smoking and obesity have also been blamed.
Dr Belloc said: "Our research proves for the first time that there is a strong paternal age- related effect on IUI outcomes, and this information should be considered by both doctors and patients."
BACKGROUNDA NUMBER of recent studies show men are not totally immune from reproductive ageing. Five years ago, researchers at the University of California Berkeley found men become less fertile each year and
that the male biological clock begins in their 20s.
Unlike women, men lose their fertility gradually and can still be fertile in old age. The UC Berkeley team examined the sperm from nearly 100 healthy men aged between 22 and 80. They tested sperm motility – its liveliness and direction of movement, and discovered that it decreases by 0.7 per cent each year.
This means that the chances of sperm being clinically abnormal or unhealthy is 25 per cent at 22 years of age. By 30 that figure jumps to 40 per cent, rising to 60 per cent at 40. At the age of 60, 85 per cent of sperm is clinically abnormal.
