Women aren’t the only ones putting off having children in the United States these days. The average age of fathers has also increased—by three and a half years over the past four decades, according to a new study in Human Reproduction.
The average paternal age at the time of an American child’s birth rose from 27.4 in 1974 to 30.9 in 2015. Over that same period, the percentage of dads over 40 when their children were born more than doubled—from 4.1% to 8.9%—and the percentage over 50 grew from 0.5% to 0.9%, according to data from all live births reported to the U. S. government from 1972 to 2015—a total of nearly 169 million babies.
Dads were older regardless of their income, their ethnicity or where they lived. Japanese and Vietnamese-American dads were the oldest overall when they had their children; on average, they were about 36 at the time of their children's births. Also, the more education dads had, the more likely they were to have children later, with college-educated new dads averaging 33.3 years old.
Plenty of research has documented the growing ages of mothers , says co-author Dr. Michael Eisenberg, assistant professor of urology at Stanford University, but until now there was little data on men to match. From a fertility standpoint, the window in which men can bear children is much larger than for women. The youngest father in the study was 11 and the oldest was 88, and Eisenberg says there is documentation of a man in India who fathered children at 94 and 96.
But the increase in fathers’ ages could still have implications for society and public health. “I think there can be good and bad to having a father who waited longer to have kids,” says Eisenberg. “On the plus side, he may be better educated, better set in his career, and have more resources and potentially more time to devote to kids.”
On the other hand, men acquire about two new mutations in their sperm DNA each year—out of billions of DNA letters. It's not clear yet whether the mutations have an impact on their children, but some studies have found links between older fathers and higher rates of autism, mental illness, some pediatric cancers, and rare genetic conditions in their children. Women with older male partners also tend to have higher rates of miscarriage, and may have a harder time becoming pregnant.
“These things are more concerning on a population level than on an individual level,” says Eisenberg. “I tell patients it’s like buying two lottery tickets instead of one. Your chances might double, but it’s still probably not going to happen.”
The new study looked at the average age of mothers as well, and confirmed trends found in previous studies. Maternal age has increased even more than paternal age in the last four decades—from 24.7 in 1972 to 28.6 in 2015—which has subsequently narrowed the age gap between moms and dads.
Eisenberg says the reasons men are delaying childbirth are likely the same as they are for women: contraception has become more widespread, there are fewer unplanned pregnancies, and career-minded couples are deciding together to start their families later.