A new study found the age of newborns’ fathers in the United States has grown several years over the last 40 years. Investigators at Stanford University School of Medicine conducted the study, who analyzed federal birth records and found a 3.5-year increase in the average age of new fathers over the past four decades.

The researchers said men over the age of 40 now account for 9 percent of all U.S. births, while men over the age of 50 account for about 1 percent.

Image credit: Sally Anscombe / Getty Images / CNBC
Image credit: Sally Anscombe / Getty Images / CNBC

Furthermore, the percentage of births to fathers older than 40 years old has more than doubled, from about 4 percent in 1972 to 9 percent in 2015. The study has not been published online yet, but it will be available in Human Reproduction on April 30.

Men are waiting longer to father children in the United States

The researchers noted the pattern is not so surprising, as similar numbers have also been seen among women. Senior researcher Dr. Michael Eisenberg said that the changing demographics of American fathers are not as studied as demographics for American mothers.

“I think it’s important for us to pay attention to these demographic shifts and what their implications could be for society,” said Eisenberg, an assistant professor of urology at Stanford University, according to CBS News.

The new study is the first comprehensive analysis of all live births reported to a federal data depository in the U.S. from 1972 to 2015, accounting for 168,867,480 births. The researchers acquired the data from the National Vital Statistics System, a data-sharing program funded by the Centers for Disease Control and Prevention.

The National Vital Statistics System records births and infant mortality rates reported by all 50 states. It also includes self-reported maternal and –if available—paternal ages, race, and ethnicity of the parents and levels of education. The CDC periodically reports on maternal statistics, but no information about newborns’ fathers is periodically released.

Older fatherhood is associated with autism, schizophrenia, cancer, and rare genetic diseases

The researchers found the average paternal age at the time of an American child’s birth has grown from 27.4 years in 1972 to 30.9 years in 2015. They noted that Asian-American fathers (mainly Japanese- and Vietnamese-American fathers) are the oldest, with an average age of 36. The median age also rose depending on the level of education, as researchers reported the typical newborn’s dad with a college degree is 33.3 years old.

Between 1972 and 2015 the rate of newborns’ fathers who were older than 40 doubled from 4.1 percent to 8.9 percent. Meanwhile, the rate of fathers who were over 50 years of age increased from 0.5 percent to 0.9 percent.

Image credit: Getty Images / TIME
Image credit: Getty Images / TIME

Similar trends of increasing average age among newborns’ dads have also been reported in other industrialized countries, according to the researchers. Eisenberg noted these new trends are likely to have an impact on public health. Meaning, an increasing paternal age can affect the total number of children a father will have, thus affecting the demographics of the population.

Moreover, Eisenberg noted that every potential father acquires an average of two new mutations in his sperm each year. Plus, there are associations between older fatherhood and higher risks and rates of autism, schizophrenia, chromosomal abnormalities, pediatric cancers and some rare genetic conditions.

On the bright side, Eisenberg said older dads are more likely to have better jobs and resources, they are more likely to have reasonably stable lifestyles and more likely to live with their kids, making them more involved in child-rearing.

Older parents could result in fewer people in the coming generations

Eisenberg noted the trend is also seen among women, not just men. In fact, he noted maternal ages at birth had advanced even more than paternal ages have in the same period.

“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,” said Eisenberg, according to EurekAlert. “The result is that the average age difference between moms and dads has been shrinking, from 2.7 years in 1972 to 2.3 years in 2015.”

The researchers noted the pattern appears to apply to all racial, ethnic, regional, age and education categories. Eisenberg said the increase in parental age is likely to exert an effect of reducing the average family size, which could have potentially massive economic ramifications. Plus, advancing parental age leaves fewer years to procreate.

“Fewer people being born means fewer productive workers a generation down the road,” he said. “This can obviously have profound tax and economic implications.”

Eisenberg noted some parental data in some states was “spotty” in the early years of the studied period, but the data for mothers has been 100 percent available for mothers since 1985. However, in 2015, information about newborns’ dads was missing in one of every nine births. He noted that could have been due because the father was unknown or because the mother didn’t want to report his name or details about him.

But it’s important that every piece of information is available, both maternal and paternal details. Eisenberg said young children whose paternal data appeared in their birth records had better health outcomes.

The researchers said the youngest father recorded during the 44-year period analyzed in the study was 11 years old, while the oldest was 88. Eisenberg said the record-holder is a man from India who early this decade fathered two babies at the age of 94 and 96 with a wife who was in her late fifties.

Source: EurekAlert!