Men in the U.S. are waiting longer than ever before becoming fathers, with the average new dad now nearly 31 years old. That’s more than three years older than a new dad was in the 1970s and tracks a similar trend among women, where the average age of first-time moms has been rising in part because of a drop in teen pregnancies.

So, besides giving men more time to sculpt their dad bods and come up with more ways to embarrass their kids, are there any implications from this? Plenty, scientists say, and not all of them good.

Stanford University researchers looked at live birth data from 1972 to 2015 and found the average age of new fathers has been climbing and varies by race, region and education level. College-educated men in northeast and western states had higher paternal ages. Japanese and Vietnamese-American new dads were the oldest, on average 36, while African-American fathers were the youngest, at 30.

The effects of older fathers on offspring health can be significant. As men age, the quality of their semen declines. Numerous reports have found increased risk of autism, psychiatric illness, pediatric cancer and chromosomal abnormalities in children born to older fathers.

The study also found benefits to having an older dad. Fathers ages 35 to 44 were more likely to live with their kids and were more involved in child rearing than fathers ages 15 to 24. Evidence also suggests the presence of the father’s name on the child’s birth certificate was associated with improved fetal health and lower infant mortality, though no one could say why. It was one of the areas the researchers said deserved more study as they explore this growing trend.