A flurry of new genetic and epidemiological studies is chipping away at a much-cherished male fantasy: Sperm, it turns out, don't age as well as some men imagine.
At least 20 exceedingly rare but potentially devastating genetic disorders, including dwarfism and other skeletal deformities, have now been linked to older fathers. Men who have families later in life also have a higher risk of fathering children with schizophrenia, studies show.
And in the latest reality check, researchers last week reported that men over 40 are nearly six times as likely to have an autistic child as those under 30.
"The conventional wisdom is clearly inaccurate: Men have as important a biological clock as women for having healthy babies," says Dr. Dolores Malaspina of Columbia University, one of several researchers examining this so-called "paternal age" effect.
Despite the gloomy statistics, scientists stress that the vast majority of children born to men of all ages are healthy, and that the deterioration of sperm over time isn't nearly as precipitous as that of human eggs. Down syndrome, for example, occurs in fewer than 1 in 1,000 women under 30. At 35, the risk jumps to 1 in 400.
By 50, it's 1 in 6.
Here's the trend
More men are putting off first-time parenthood -- or, in some cases, fathering new broods with younger spouses. Since 1980, U.S. birth rates have shot up as much as 40 percent for men aged 35 to 49. Meanwhile, they've decreased up to 20 percent for men under 30, according to the National Center for Health Statistics.
As a result, some scientists say it's important that men understand that there are potential consequences to becoming latter-day dads.