Biological Clocks Tick for Men, Too

July 7, 2008— -- A new study shows that a man's fertility starts to fall in his mid 30s, providing more evidence that like women, men, too, have a kind of biological clock that can play a big role in a women's chances of getting pregnant.

Researchers in France found that a male's fertility starts to decline as he enters his mid-30s and is significantly lower if he is over 40.

The study included more than 12,200 couples being treated for infertility at the Eylau Center for Assisted Reproduction in Paris. The women were given intrauterine inseminations, or IUIs, also known as artificial inseminations, where sperm is inserted into the uterus when the woman is ovulating. This type of treatment is typically given to couples if the woman has no fertility problems.

Scientists monitored more than 21,000 of these procedures between January 2002 and December 2006 and recorded rates of pregnancy, miscarriage and births.

If a woman was over 35, the rate of pregnancy was lower. This was expected: maternal age has been long been linked to a couple's rate of pregnancy and chances of miscarriage.

But the study also found that if the father was in his late 30s, the chances of a successful pregnancy went down. Ten percent of treatments led to pregnancy in fathers over 40.

The father's age also affected rates of miscarriage. If a father was over 34, the miscarriage rate was 16.7 percent. Between the ages of 35 and 39, it went up to 19.5 percent. And if the father was older than 44, it jumped to 32.4 percent -- which means nearly one-third of the pregnancies ended in miscarriages.

Researchers said the problems were likely the result of DNA damage and fragmentation in sperm, which can lead to pregnancy failure and miscarriage.

Dr. Peter Schlegel, chairman of urology at the Weill Cornell Medical Center in New York, works at the Male Center for Reproductive Medicine. He told ABC News it is possible that there is a link between DNA damage and age.

"As men get older, there is an increase in the risk of having that fragmented DNA," Schlegel explained.