A new study has revealed that rates of pregnancy in women drop and risk of miscarriage increase if the father is over 40.
It has long been known that a woman's chance of reproducing declines with age once she is in her mid-thirties, but the new findings provide the strongest evidence to date that being an older father poses a risk as well.
Researchers in France monitored 21,239 cases of intrauterine insemination (IUI) -- a particularly effective type of artificial insemination -- in more than 12,000 couples.
As expected, they found that women over 35 showed significantly decreased pregnancy rates compared to younger women, as well as higher rates of miscarriage.
"But we also demonstrated that the age of the father was important in the rate of pregnancy, with a negative effect for men over 40," said Stephanie Belloc, a researcher at the Eylau Centre for Assisted Reproduction in Paris, and lead author of the study.
"And even more surprising, the proportion of miscarriages went up as well," she added.
Belloc was to present her research Monday at the annual meeting of the European Society of Human Reproduction and Embryology in Barcelona. They will be published in the British journal Reproductive Biomedicine.
In IUI treatment, sperm are separated from seminal fluid in a centrifuge. The "washed" sperm are then inserted directly into the uterus in order to enhance the chances of conception.
In most of the cases examined, the couples were being treated because of the husband's infertility, but the findings also apply to men without such problems, the researchers said.
"There is no doubt that we can extrapolate from the study to men in general," said co-author Yves Menezo, also a researcher at the Eylau Centre.
Although previous research has shown an overall decline in sperm count and quality as men age decade by decade, this is the first clinical proof that simply being an older man has a direct effect on a couple's fertility, he said.
"We already believed that couples where the man was older took longer to conceive," said Belloc in a statement. "But how DNA damage in older men translates into clinical practice has not been shown up to now."
The impact of paternal age on artificial insemination outcomes "should be considered by both doctors and patients in assisted reproduction," she added.