07/16/2008 05:12 am ET Updated Nov 17, 2011

A Blow to the Potency of Middle-Aged Men

The assumption has always been that men could father children long after women the same age have been forced to hang up their reproductive shoes.

That's because men always have a fresh supply of sperm, while a woman's eggs are as old as she is. After 35 or so, eggs start to show their age.

But according to a new study, the news is no longer so bright for older men.

Researchers at a French reproduction clinic performed 21,239 intrauterine inseminations, and collected detailed stats on the outcomes. The pregnancy rates for men under 35 were 14.4 percent, but dropped to 9.3 percent after age 45, says Dr. Stephanie Belloc of the Eylau Centre for Assisted Reproduction in Paris. "And, perhaps more surprisingly," Belloc said in a statement, "miscarriage rates increased where the father was over 40."

The study, presented on July 7th at the annual conference in Barcelona of the European Society for Human Reproduction and Embryology, is the first, Belloc says, to show an effect of paternal age on pregnancy and miscarriage rates.

Both pregnancy and miscarriage rates are affected by mothers' age, too, but, until now, the blame for the problems has fallen almost exclusively on mothers.

Now, men might be a little less glib about their ability to have children whenever they like. Clearly, something in the male machinery falters with age, too. And this is a failure Viagra won't help.