(CN) – Fathers of newborns born in the United States today are 3.5 years older on average than they were four decades ago, according to a new study.
A review of more than 168 million births between 1972 and 2015 reveals that parents in the United States are waiting longer to begin families, which mirrors trends in other industrialized nations.
Published Wednesday in the journal Human Reproduction, the report finds that the average paternal age at time of birth rose from 27.4 years old to 30.9 years old, with the age of fathers increasing with more years of education.
Fathers over the age of 40 more than doubled – from 4.1 percent to nearly 9 percent – over the period reviewed. Men over the age of 50 now account for nearly 1 percent of fathers, up from 0.5 percent in 1972.
Senior author Michael Eisenberg said older fathers are more likely to live with their children, have better jobs and enjoy reasonably stable lifestyles. These factors lead to fathers generally being more involved in child-rearing.
The steady increase in the average age of fathers will also have public health implications, according to Eisenberg. He noted that “every potential dad acquires an average of two new mutations in his sperm each year.”
Associations between older fatherhood and higher rates of autism, schizophrenia, chromosomal abnormalities, some pediatric cancers and rare genetic conditions have been observed, he added.
Maternal ages have increased as well – more than paternal ages, according to the study.
“This may be a consequence of women waiting longer to get married or putting off childbearing as the years they spend in higher education increase and as careers become more central to their lives,” Eisenberg said.
The average age difference between moms and dads has decreased from 2.7 years in 1972 to 2.3 years in 2015. This pattern seems to apply to all regional, racial, age and education categories.
“We’ve seen a lot of changes in the last several decades,” Eisenberg said. “Contraception is more reliable and widespread. Women have become more integrated into the workforce. This seems to be reflected in an increasing parity in parental ages over the last four decades.”
With older families producing fewer children over a shrinking window of possible childbearing, the increasing average ages of parents could also have a pronounced effect on the economy.
“Fewer people being born means fewer productive workers a generation down the road,” Eisenberg said. “This can obviously have profound tax and economic implications.”
Reporting of maternal data by states improved over the period reviewed by the study, reaching virtually 100 percent since 1985. However, paternal information was still missing in one of every nine births in 2015, possibly because the father was unknown or because the mother did not want to report his name or information, Eisenberg said. Mothers self-report paternal data.
The team says evidence suggests that, on average, children whose paternal data is listed in their birth records have better health outcomes.
The oldest father recorded during the period reviewed was 88 years old, while the youngest was 11.
A man from India holds the record for the oldest man to father a child at the age of 96, according to Eisenberg. The mother in that case was in her late 50s.
Asian-American fathers are the oldest on average, at upward of 36 years old.
The study is based on data from the National Vital Statistics System, an intergovernmental program sponsored by the U.S. Centers for Disease Control and Prevention.