“For genetic abnormalities, it’s not just a woman’s problem anymore,” says Harry Fisch, a professor of urology at Weill Cornell Medical College and the study’s lead author. “The fact that couples are waiting longer to have children makes this very significant.”
But the combined test takes only maternal age into consideration, in part because paternal age hasn’t yet been studied enough for it to be accurately used as a risk factor. A father’s age has long been recognized as a factor in relatively rare genetic conditions like Klinefelter syndrome and achondroplasia, or dwarfism—but it’s only in the last 15 years or so that it’s started to receive more research attention, as studies have shown that it may also play a role in better-known conditions like autism and schizophrenia.
“The question is, why aren’t more people looking into this? There’s still much more interest in maternal issues than paternal issues. It takes a long time for a paradigm shift in the way we think,” Fisch says.
While women who have children at age 35 or older are considered to be of “advanced maternal age,” the medical community has yet to define “advanced paternal age,” according to the geneticists Helga Toriello and Jeanne Meck, who co-authored a guideline for genetic counseling for older fathers. “Some studies look at [men] over 40, some over 50, some over 35,” Toriello says. Though research suggests that the paternal-age effect is most significant for fathers over 40, younger fathers may also face an increased risk, possibly because spermatogenesis in very young fathers is more likely to result in the same mutations seen in older fathers. A recent study suggests that a 20-year-old father doubles the chance of Down syndrome as compared to one who’s 40.
But until more is known about the effect of paternal age, it’s difficult to know the true accuracy of the current combined test for Down syndrome. A woman who’s 49 has a one-in-nine chance of having a baby with Down syndrome—but the test doesn’t account for fluctuations in that number based on whether her partner is 24 or 64. And because women often partner with men older than they are, it’s also not clear now much paternal age may have already silently influenced the risk that the combined test assigns to each additional year of a mother’s life.
“You would need to take those 49-year-old women and those that have a 20-something-year-old partner and those that have a 30-year-old partner [and so on] and see what the differences might be,” Toriello says. Fisch’s study comes the closest, but no one has replicated that study with a bigger sample size.
The most accurate risk assessment would take both the maternal and paternal contribution into account, adjusted for the combined age of the mother and the father. “It’s not a maternal issue, it’s not a paternal issue. It’s a parental issue,” Fisch says. “It’s no longer one or the other.”