Women are constantly reminded of their ticking biological clocks and the risks that come with having children later in life — both in terms of maternal and infant health, and the ability to conceive a baby in the first place. But for the most part, men don’t get the same warnings.
A new study published Wednesday in the BMJ suggests that men, too, may have biological clocks worth heeding. Babies born to older fathers, the paper says, may be more susceptible to health problems including preterm birth, low birth weight and breathing problems. And women who have children with older men may have increased health risks, too — particularly gestational diabetes.
“From an evolutionary standpoint, we’re used to reproducing in the late teens, early twenties,” says study co-author Dr. Michael Eisenberg, director of male reproductive medicine and surgery at Stanford University Medical Center. “Anything beyond that may have some potential biologic risk associated with it.”
Despite our evolutionary roots, American women are increasingly having babies later in life, in part because many are pursuing careers and education before starting families. Paternal age seems to be following the same pattern. Between 1972 and 2015, the average age of fatherhood rose from 27.4 to 30.9 years old, and the percentage of fathers over 40 rose to about 9%, a 2017 study found.
Much has been made of the health issues associated with “geriatric pregnancies,” such as higher odds of preterm birth, low infant birth weight and gestational diabetes and high blood pressure for the mother, both of which can affect infant development and lead to complications. Eisenberg and his colleagues set out to determine if similar dangers applied to older fathers.
Using data from the National Vital Statistics System, they analyzed the more than 40 million live births that occurred in the U.S. between 2007 and 2016. (During this time period, the average age of fathers rose from 30 to 31.2 years.) They sorted the fathers of these babies into five age groups — younger than 25, 25-34, 35-44, 45-54 and older than 55 — and looked at measures of infant health within each of these categories.
After accounting for things like the mother’s age and the parents’ health and demographic information, the researchers noticed an association between paternal age and likelihood of both child and maternal health problems. Significant associations began to surface around age 45, and the data suggest that the older the father, the higher the risks.
Compared to infants born to men ages 25 to 34, babies with dads older than 45 tended to weigh less and had a 14% higher chance of premature birth. Babies born to men older than 55 also tended to score lower on the Apgar test, a measure of newborn health that assesses things like heart rate, breathing and reflexes. These babies also had a 10% higher risk of needing breathing assistance and a 28% higher chance of being admitted to the neonatal intensive care unit, the researchers found.
Women with partners older than 45 were also 28% more likely to develop gestational diabetes, compared to women with partners ages 25 to 34, the paper says.
The new study joins past research that has linked higher paternal age with mental and behavioral health issues in children such as autism, attention-deficit hyperactivity disorder and bipolar disorder. While the reasons for these associations, as well as those detailed in the new paper, aren’t totally clear, they may have something to do with spontaneous genetic mutations that occur throughout a man’s life, research suggests.
Men are continuously making sperm, Eisenberg explains, meaning their cells are constantly dividing and renewing. Occasionally this process goes awry, leading to approximately two random genetic mutations each year. The older a man is, the more of these mutations he’s accumulated over time, and the greater his chances of passing down a harmful mutation, Eisenberg says. Older men may also have experienced more epigenetic changes, or modifications to DNA caused by environment or lifestyle, than younger men, he adds.
Eisenberg stresses that the absolute risk of infant health issues is still small, even if the likelihood increases with paternal age. He likens the odds to buying lottery tickets: Your chances get better if you buy two, but it’s still a long shot.
Still, Eisenberg says accumulating evidence suggests that men should think carefully about when they have kids. “Most of the risk with being an older parent probably applies more to women than men, but I think this shows that you shouldn’t forget the man,” he says. “Men shouldn’t think of the runway as unlimited.”