MONDAY, July 7 (HealthDay News) -- Among couples with fertility problems, those in which the man is over age 35 have lower pregnancy rates and increased chances of miscarriage, a new study shows.

To come to this conclusion, French researchers looked at more than 12,000 couples who went to a fertility clinic in France.

In most of the cases, the couples were being treated due to the man's infertility. The couples underwent a total of 21,239 intrauterine inseminations (IUIs).

The researchers found that women over age 35 had a pregnancy rate of 8.9 percent, compared to 14.5 percent in younger women.

"But we also found that the age of the father was important in pregnancy rates -- men over 35 had a negative effect. And, perhaps more surprisingly, miscarriage rates increased where the father was over 35," study author Dr. Stephanie Belloc, of the Eylau Center for Assisted Reproduction in Paris, said in a prepared statement.

This is the first study to document such a strong paternal effect on reproductive outcomes. The findings were presented Monday at the European Society of Human Reproduction and Embryology annual conference, in Barcelona.

"How DNA damage in older men translates into clinical practice has not been shown up to now. 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 in assisted reproduction outcomes," Belloc said.

"We believe that the use of IVF or ICSI should be suggested to infertile patients where either party is over 35 years of age," she added.

More information

The American Society for Reproductive Medicine has more about infertility.