When it comes to ticking biological clocks, it's women that first spring to mind. Sure, advancements in science have made it possible for women to conceive beyond age 40, but not without increased risks and concerns. But now, it seems men too may have reason to worry about their own reproductive window of opportunity.

Stephanie Belloc, a researcher for the Eylau Centre for Assisted Reproduction in Paris, discovered that age is an important factor in the quality of men's sperm. The research team issued a news release in which they reported to have "found that the age of the father was important in pregnancy rates - men over 40 had a negative effect. And, perhaps, more surprisingly, miscarriage rates incrased where the father was over 40."

This latest research seems to have thrown a monkeywrench into the conventional wisdom that men can have babies just about any time they want, and puts a new spin on the older man/younger woman matchups. According to Belloc, "This research has important implications for couples wanting to start a family."