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.
Previous studies have shown that the risk of a woman having a baby with Down syndrome rises dramatically after she reaches 35. Although this effect of maternal age on Down syndrome risk is well known, researchers say the influence of the father's age on Down syndrome has not yet been defined. Some studies have found no relationship, while other, smaller studies have suggested that older fathers may raise the risk of Down syndrome.
But researchers say this study, published in The Journal of Urology, is the largest of its kind and looked at 3,429 Down syndrome cases reported to the New York State Department of Health from 1983 to 1997. Their findings suggest that the increase in the number of babies with the genetic abnormality born to women over 35 may be the result of a combined effect of both advanced maternal and paternal ages.
Older Fathers Face More Risks
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.
In fact, researchers suggest that there is only a modest increase in Down syndrome risk for women 35-39 compared with women 30-35 years old, but the dramatic increase in Down syndrome births among women 35 to 39 years old is largely due to the influence of older fathers because older women tend to make babies with older men.
Although more research is needed to confirm these findings, researchers say the study shows that the father's age should not be ignored in family planning.
"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," conclude the authors.