Women are constantly reminded of their ticking biological clocks and the risks associated with later childhood, both in terms of maternal and child health and the ability to conceive a child at all. Mostly, however, men do not receive the same warnings.

A new study was published on Wednesday in the BMJ suggests that even men can have biological watches to watch out for. Babies born from older fathers may be more susceptible to health problems, including prematurity, low birth weight and respiratory problems, according to the newspaper. Women who have children with older men may also have an increased health risk – especially gestational diabetes.

"From an evolutionary point of view, we are used to reproducing in the late twenties, early twenties," says study author Dr. Michael Eisenberg, director of male reproductive medicine and surgery at Stanford University Medical Center. "Anything beyond this can bring with it a potential biological risk."

Despite our evolutionary roots, American women increasingly have babies later in life, partly because many pursue a career and education before founding a family. The paternal age seems to follow the same pattern. Between 1972 and 2015, the average paternal age increased from 27.4 to 30.9 years, and the percentage of over-40s increased to about 9%. This was the result of a study from 2017.

Much has been said about the health problems associated with geriatric pregnancies, such as a higher likelihood of premature birth, low birth weight and gestational diabetes, and high blood pressure for the mother, both of which can interfere with the development of the child and lead to complications. Eisenberg and his colleagues wanted to find out whether similar dangers apply to older fathers.

Data from the National Vital Statistics System analyzed the more than 40 million live births that occurred between 2007 and 2016 in the United States. (During this period, the average age of the fathers increased from 30 to 31.2 years.) Fathers of these babies in five age groups – younger than 25, 25-34, 35-44, 45-54 and older than 55 years – and examined the measures the health of children in each of these categories.

After taking into account the age of the mother and the health and demographic information of the parents, the researchers found a correlation between the age of the parents and the likelihood of health problems of children and mothers. By the age of 45, significant associations emerged, and the data suggest that the older the father, the higher the risk.

Compared to infants born to men between the ages of 25 and 34, babies with fathers over 45 years of age tended to weigh less and had a 14% higher risk of premature birth. Babies born to over 55-year-olds tend to be lower in the Apgar test, a measure of neonatal health that rates factors such as heart rate, respiration, and reflexes. These babies also had a 10% higher risk of requiring respiratory support and a 28% higher chance of being admitted to the neonatal intensive care unit.

Women with partners older than 45 years were also 28% more likely to develop gestational diabetes compared to women with partners aged 25 to 34 years.

The new study follows previous research that has linked a higher age of paternal patients to mental health and behavioral health problems in children such as autism, attention deficit hyperactivity disorder, and bipolar disorder. Although the reasons for these associations, as well as those described in the new work, are not very clear, they may have something to do with spontaneous genetic mutations that occur in a man's life, according to research.

Men are constantly making sperm, explains Eisenberg, which means that their cells constantly divide and renew. Occasionally this process goes awry and leads to about two random genetic mutations each year. The older a man is, the more mutations he has accumulated over time, and the greater is his chance of overcoming a harmful mutation, Eisenberg says. Older men may also have experienced more epigenetic changes or changes in DNA through the environment or lifestyle than younger men, he adds.

Eisenberg emphasizes that the absolute risk to the health of infants is still low, even if the probability increases with the age of the father. He compares the odds with buying lottery games: your chances will be better if you buy two, but it's still a long way to go.

Eisenberg says, however, that gathering evidence suggests that men should carefully consider when they have children. "The biggest risk of being older parents is probably affecting more women than men, but I think that shows you should not forget the man," he says. "Men should not consider the runway to be unlimited."

Write to Jamie Ducharme at jamie.ducharme@time.com.



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