The greater incidence of Down syndrome in the children of older mothers has made us aware of risks to the fetus during pregnancy as women age. Now we are learning that birth defects are also more frequent as fathers get older.
The risk that a baby will be born with a birth defect is much smaller among older men than among older women. Nevertheless, more than 20 rare but devastating genetic disorders have been linked to aging fathers. In addition, older men have more problems with fertility than do younger men, and women of all ages have more miscarriages if their partner is 35 years of age or older.
A recent study of over 300,000 parents in Israel found a six-fold greater risk of autism in children whose fathers were age 40 or older compared to those whose fathers were 30 or younger.
DNA damage in sperm is one probable explanation for the genetic abnormalities associated with fatherhood at an older age. The testicular cells that give rise to sperm divide every 16 days; this means that the cells will have split about 840 times by age 50, and with each cell division the chance increases for errors in the sperm's DNA. Examination of sperm from men ages 22 to 80 showed a progressive increase with age in the number of broken DNA strands and other genetic abnormalities.
These results should not discourage men of all ages from having children. However, parents-to-be should recognize that younger adulthood is the best time for both sexes to have children. Yet the trend is just the opposite in this country. Since 1980, birth rates among men between the ages of 35 to 49 have skyrocketed by about 40 percent, while they have fallen by about 20 percent for men under age 30.
