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SATURDAY, June 12 (HealthDayNews) -- For years, women of a certain age -- say, 35 and older -- have listened anxiously to the ticking of their biological clocks, mindful that with each passing birthday their fertility was decreasing and their chances of producing a baby with a birth defect was increasing.

Now, it's the guys' turn to pay attention to their own biological clocks.

While fertility doesn't decrease as dramatically as for a woman, a man does have a biological clock, experts say. But these scientists disagree on exactly when the alarm sounds.

In general, "there's a decline in testosterone of about 1 percent per year for men after age 30," said Dr. Harry Fisch, director of the Male Reproductive Center at Columbia University in New York City. But it's difficult to pinpoint which men will have trouble conceiving a child with a birth defect based on age, he said. "The problem is the biological clock ticks at different speeds for different men," he explained.

While Fisch encourages men who want to be fathers to do so "sooner rather than later," another fertility expert contends there's not a big rush. The loud ticking of the clock doesn't usually begin until a man is in his 50s, said Dr. Larry Lipshultz, chairman of the American Urological Association's Council on Reproductive Health.

"As a man gets over 50, his sperm count decreases statistically but not clinically significantly," Lipshultz said. In other words, a test could detect the decline, but a man could still easily become a father.

"Men will always make sperm," Lipshultz added. "In that sense, there is not the same biological clock" as for women, who have no more eggs left by menopause.

The notion that men have a biological clock isn't entirely new, as a medical perspective article published in the April 14 issue of the Journal of the American Medical Association noted.

As early as 1912, a doctor named Wilhelm Weinberg found an inherited skeletal disorder called achondroplasia occurred more often in younger siblings than older ones, suggesting that as men aged, the probability of passing on the disorder increased.

And in recent years, several studies have uncovered some other risks linked to late fatherhood.

For instance, Fisch and his colleagues looked at more than 3,400 cases of Down syndrome, a congenital defect caused by an extra chromosome that results in mental and physical abnormalities. They found the father's age played a role if the woman and the man were both over 35 when conceiving.

The effect was most pronounced when the woman was over 40, Fisch found. In those cases, "we found the incidence of Down syndrome is approximately 50 percent related to sperm," Fisch said. His research appeared in the June 2003 issue of The Journal of Urology.

Another study, published in 2001 in the Archives of General Psychiatry, found the risk of schizophrenia in children was associated with older paternal age. For instance, children of fathers over 50 were almost three times more likely to have schizophrenia than children born to the youngest fathers, the research found. The database included nearly 90,000 people.

Approximately 20 different disorders are now correlated with a father's age, according to the April 14 perspective piece in JAMA.

Another study, published in June 2003 in Fertility and Sterility, found it takes up to five times longer for a man over 45 to get a woman pregnant than if he is under 25.

As men age, Fisch said, "their sperm are more at risk of not just [having] genetic problems but of decreased ability to fertilize the egg."

"As you age, you will have worse sperm and more genetic abnormalities," Fisch said. "If you want to have kids, have them sooner."

But with people who marry later in life, hoping to achieve career and financial stability before starting a family, Fisch knows early fatherhood isn't always that easy.

If fatherhood has to be delayed, Fisch advises men to stay in as good physical shape as possible.

Lipshultz offers men a bit more latitude. "The studies I have seen put the cutoff in the 50s for significant increases in the chances of genetic defects," he said.

The healthiest time for a man to conceive? "I would think before 50, but that's my own personal experience," based on his work with patients, Lipshultz said.

For a man, Lipshultz said, "the clock never stops. It just slows down."

More information

To learn more about the male biological clock, visit the American Society for Reproductive Medicine and the University of Texas Health Science Center at San Antonio.

(SOURCES: Harry Fisch, M.D., director, Male Reproductive Center, and assistant professor, urology, Columbia University, New York City; Larry Lipshultz, M.D., professor, urology, Baylor College of Medicine, Houston, and chairman, American Urological Association's Council on Reproductive Health)

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