Robert De Niro joins an exclusive club: older new fathers

How rare is it to be an older father? A 2018 study by researchers at Stanford University looked at more than 34.3 million births in the United States from 2007 to 2016 in which the father’s age was available.

Fathers who were 25 to 34 accounted for the largest share of those births, about 18.3 million, the study found. But by the age of 55, men were much less likely to be fathers. Men 55 and older accounted for only 111,130 births over the decade, according to the study, which was published in the British Medical Journal.

The study found that the average age of fathers was edging higher over the period, from 30 years to 31.2. In a previous study that looked further back in time, researchers found that the average age of fathers had risen from 27.4 years in 1972.

De Niro’s case is rare but not unprecedented. The Guinness Book of World Records lists the oldest “legal father” as a 92-year-old Australian man who had a baby in 1998. Other notable older fathers have reportedly included novelist Saul Bellow, actor Anthony Quinn, and actor James Doohan, who had children at 84, 81, and 80, respectively.

The Stanford study found an association between older fathers and a higher risk of various medical issues in children, including prematurity, low birthweight, need for ventilation, and need for intensive care. But the study’s senior author said in a statement that the overall risk to children was still relatively low.

Dr. Martin Kathrins, chief of reproductive medicine at Brigham and Women’s Hospital, said Wednesday that research has also suggested that the children of older fathers have increased risks for neuropsychiatric problems, including schizophrenia and autism.

He said he tells prospective fathers who are older that “these remain uncommon problems for people, but the children you have will have a higher risk” of them. He said he has seen men in their 70s who want to have babies but it’s rare.

He said the exact causes of medical problems among children of older fathers remain a mystery. “Nobody really understands why this is,” he said.

“We’re learning more about the risks of advanced paternal age,” he said. “This is an area of some active research focus.”

The increase in fathers’ ages parallels a rise in mothers’ ages. Birthrates have declined for women in their 20s and jumped for women in their late 30s and early 40s, according to a report last year from the US Census Bureau.

Older mothers — those 35 or older — are at higher risk of pregnancy complications and of passing on certain chromosomal conditions, such as Down syndrome, to their children, according to the Mayo Clinic.

Material from The Associated Press was used in this report.

Martin Finucane can be reached at martin.finucane@globe.com.