Fathers Age Responsible for up to 50% of risk of Down Syndrome if the Mother is also over 40

July 1, 2003 -- Older fathers may contribute just as much as older mothers to the dramatic increase in Down syndrome risk faced by babies born to older couples. A new study found that older fathers were responsible for up to 50% of the rise in Down syndrome risk when the mother was also over 40.

Researchers say the number of births to parents over age 35 has more than doubled in the last 20 years and this has raised questions about the role of paternal age in the risk of genetic abnormalities and birth defects.


The study showed that the percentage of births to women over 35 grew from 8% of all births in 1983 to 17% in 1997, and the greatest change during this period was the number of births to mothers and fathers over 40 years old, which rose by 178% and 73%, respectively.


Researchers found that the rate of Down syndrome among parents over 40 was 60 per 10,000 births, which is six times higher than the rate found among couples under 35 years old. Older fathers over 40 had twice the rate of Down syndrome births compared with men 24 years old and younger when they had children with women over 35.


"Paternal age has an effect on Down syndrome but only in mothers 35 years old and older," write researcher Harry Fisch, MD, of the department of urology at Columbia-Presbyterian Medical Center in New York City, and colleagues. "In younger women, in whom age was not a risk factor for Down syndrome, there was no paternal effect."


Among older mothers over 40, researchers found that an increase of 50% in Down syndrome risk was attributable to the advanced age of the father.






"Young couples preparing for family planning must be aware that advanced parental age may not only result in increasing difficulties with fertility for the parents but that children born to older parents may be at higher risk for genetic abnormalities,"