Newborns of fathers 45 and older are more likely to be underweight or wind up in intensive care, researchers reported Thursday, adding to the list of problems associated with older dads.
For fathers 55 and up, infants tended to score worse in a standardised test used to assess the baby's health immediately after birth.
Even more startling -- and harder to explain -- was a heightened risk for women carrying the child of a man 55 and older of diabetes arising during pregnancy, according to a study published in the medical journal BMJ.
All these conclusions, the researchers cautioned, are based on an analysis of medical records rather than a controlled experiment, which means no firm conclusions about cause-and-effect can be drawn.
The overall risk of such outcomes also remained low, they added.
But the findings held true even after other factors that might skew the results -- age of the mother, maternal smoking, level of education -- were taken into account, they said.
"A significant number of these negative birth outcomes were estimated to be prevented if older fathers had elected to have children before the age of 45," the scientists concluded.
"The risk associated with advanced paternal age should be included in discussions regarding family planning and reproductive counselling."
The average age of fatherhood has been steadily rising in wealthy nations, as has the percentage of fathers above 45 or 55.
In the United States, the number of births to men 40 and older has almost doubled to nine percent over the last 40 years. For men over 50, the percentage has gone up from 0.5 to nearly one.
20 grammes lighter
Similar trends are found in western Europe. In England, for example, fathers over 35 accounted for 40 percent of all births in 2003, compared with 25 percent in 1993.
To date, most research on the link between the age of parents and health outcomes in children has focused on older mothers.
But recent studies suggest that being a father later in life may also be associated with higher risks in offspring of autism, genetic abnormalities and mental problems.
One possible culprit is thought to be changes with age in male reproductive cells that affects the way genes are expressed, rather than the genes themselves.
To better understand the possible impact of advanced-age fatherhood on infants and mothers, researchers led by Michael Eisenberg of Stanford University combed through data on more than 40.5 million births in the United States from 2007 to 2016.
Children born of fathers 45 or older were on average 20 grammes lighter, and had a 14 percent higher risk of low birth weight -- less than 2.5 kilos (5.5 pounds) -- than infants born to younger dads.
These children were also 14 percent more likely to be admitted to a neonatal intensive care unit, and had 18 percent higher odds of experiencing a seizure compared with infants of fathers aged 25 to 34.
The risk of gestational diabetes, meanwhile, for women carrying the child of a man aged 55 or older increased by 34 percent.
The researchers further estimate that 13 percent of premature births were attributable to fathers of more advanced age....