In fact, about 9 percent of all newborns in the U.S. now have dads older than 40, and almost 1 percent have dads over the age of 50.
Some level of this paternal age increase has occurred among all races and ethnicities, across all educational levels and in all geographical regions of the country.
We’ve known of a similar trend among women for quite some time. Last year, for example, researchers reported that the mean age of a woman when she first gives birth is 26.3, up from 24.9 just 15 years ago. That rise is due to a variety of factors: improved contraception, better access to higher education, greater assimilation into the workforce, and technologies that have extended women’s reproductive years.
Surprisingly, however, the current study is apparently the first to do a comprehensive analysis of the age of newborns’ fathers in the U.S.
For the study, researchers at Stanford University School of Medicine analyzed birth data collected from all 50 states between 1972 and 2015 by the National Vital Statistics System. The data involved more then 168 million births and included (in most cases) the self-reported ages of the mother and father, their race and ethnicity, their levels of education, and where they live.
The analysis revealed that the mean age of the fathers of newborns rose from 27.4 years in 1972 to 30.9 years in 2015.
The proportion of newborns’ fathers who were older than 40 more than doubled during that period — from 4.1 percent to 8.9 percent — while the proportion who were over 50 rose from 0.5 percent to 0.9 percent.
As the study’s authors point out, similar trends have been observed in other developed countries. In Germany, for example, the median age of fathers rose from 31.3 to 33.1 years between 1991 and 1999. And in England, the proportion of married men who became a father between the ages of 45 and 49 increased from 2.1 percent to 3.3 percent between 1997 and 2006.
“As in the USA, paternal age in these two European countries appeared to be increasing with more fathering children in the fifth and sixth decades of their lives,” the researchers write.
A widespread trend
Here are some other key findings from the study:
- The mean age of paternity was up among all races and ethnicities, although Asian-American dads tended to be the oldest, while black and Hispanic dads tended to be the youngest. Japanese-American fathers had the largest increase in mean age, from 30.7 years in 1972 to 36.3 years in 2015.
- Paternal age was also up among fathers of all education levels, although those who completed college tended to become dads at older ages (33.3 years, on average), compared to those with who went no further than high school (29.2 years).
- Fathers in all regions of the country were older in 2015 than in 1972. The Northeast had the oldest dads (31.8 years, on average), followed by the West (30.4), the Midwest (30.3) and the South (29.8). (Those numbers are from 2001-2005, the latest years for which data is available.)
Interestingly, the study also found that the mean age difference between parents shrank. In 2015, fathers were, on average, 2.3 years older than the mothers of their children, compared to 2.7 years in 1972.
The birth records also revealed that the youngest dad was 11 years old, and the oldest was 88.
The study’s findings about the aging of U.S. fathers have public health implications, the researchers point out.
“As men age, the quality of their semen declines,” they explain. “In addition to delayed time to conception, the effects of advanced paternal age on offspring health can be significant. Numerous reports have found increased risk of autism, psychiatric illness, neurologic disease such as neurofibromatosis, pediatric cancer and chromosomal abnormalities in children born to older fathers.”
Of course, having an older father can also be beneficial to a child’s well-being. A 2013 study found that men who become a dad between the ages of 35 and 44 are more likely to live with their children and are thus more involved in childrearing than men who enter fatherhood at a younger age.
There are social implications as well to advancing parental age as well. It leaves fewer years for having children, a factor that is likely to lead to smaller families.
“Fewer people being born means fewer productive workers a generation down the road,” said Dr. Michael Eisenberg, the study’s senior author and a professor of urology, in a released statement. “This can obviously have profound tax and economic implications.”
(Whether slower population growth is good or bad for the economy is currently a matter of debate, however.)
FMI: You’ll find an abstract of the study on the Human Reproduction website, but the full study is behind a paywall.