A couple’s risk of having a pregnancy end in Miscarriage appears to climb in tandem with the man’s age, study suggests.

While older women are known to have a higher risk of Miscarriage than younger ones, the effect of a man’s age has been less clear. The new study, which followed more than 5,100 pregnant women from the first trimester onward, strengthens the evidence of a connection between a father’s age and miscarriage risk, according to the study authors.

They found that, regardless of the woman’s age, a couple’s risk of Miscarriage grew steadily as the man’s age increased from 20 to 50. Overall, miscarriage risk was 27 percent greater if the man was older than 35 than if he was younger.

“Our results confirm that an influence of paternal age on the risk of spontaneous abortion is very likely to exist,” said Dr. Remy Slama, of the French National Institute for Health and Medical Research (INSERM) in Le Kremlin-Bicetre.

Slama and his colleagues in France, the U.S. and Germany report the findings in the May 1st issue of the American Journal of Epidemiology.

It’s believed that as men age, they tend to produce a greater number of sperm with chromosomal abnormalities. Chromosome defects in the fetus are responsible for a large portion of miscarriages - particularly in the first trimester - so it may be through transmission of genetic anomalies from sperm to embryo that a father’s age affects miscarriage, Slama explained. Like people, he noted, sperm “also get older.”

He and his colleagues followed 5,121 California women from the first trimester until they gave birth or the pregnancy ended. Overall, 491 women had a miscarriage after the sixth week of pregnancy.

Initially, the researchers found that a 40-year-old woman had more than three times the risk of miscarriage as a 25-year-old woman did. When they factored in the man’s age, however, the risk associated with older maternal age dipped somewhat.

“Part of the effect formerly attributed to maternal age was actually due to paternal age,” Slama said.

In general, the researchers found, miscarriage risk steadily inched upward as men grew older, doubling between the ages of 20 and 50. For women, the risk increased roughly five-fold between the ages of 20 and 45.

SOURCE: American Journal of Epidemiology, May 2005.