FORBES ON FERTILITY: FISCH, "WHY WOULD YOU THINK THE SPERM OR TESTICLES DON'T AGE?"

Allison Van Dusen, 04.11.07, 12:01 AM ET

Dr. Samuel Pang, medical director of the Reproductive Science Center of New England, estimates that about one third of his patients' difficulties is due to a woman's health problem and another third is due to a problem with a man's sperm.

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The other third consists of couples whose age is affecting their ability to conceive, a group that's growing as more people delay having children until later in life. Doctors say maternal age in particular is one of the most important factors couples need to consider.

"Sociologically we've changed, but our biology hasn't changed very much," says Dr. Richard Scott, director of Reproductive Medicine Associates of New Jersey. "Women make a lifetime supply of eggs when they're in the fetus. When they're gone, they're gone."

In fact, a woman's fertility starts to measurably decline around age 27, due to the depletion and aging of her eggs. For those under 30, it's estimated that the chance of getting pregnant in any one cycle is 20% to 30%. By age 40, it falls to 5%, according to the American Fertility Association.

Guys, Listen Up
But it's not just women who need to pay attention to the ticking of the clock, says Dr. Harry Fisch, director of the Male Reproductive Center at New York-Presbyterian Hospital/Columbia University Medical Center and author of The Male Biological Clock.

Men over 35 are twice as likely to be infertile as those under 25. Studies also are showing that, as with older women, older men are more likely to have children with birth defects due to the decreased genetic quality of their sperm.

"Every cell in the body ages," Fisch says. "Why would you think the sperm or testicles don't age?"