Advanced Paternal Age Is Rising Among US Fathers

Many people need no reminder that motherhood is limited by a biological clock. It is a reality that keeps many women awake at night, shapes decisions about careers and relationships, and accounts for a substantial share of the US$819 million IVF industry.

However, later fatherhood carries risks of its own. A new study has found that the proportion of US fathers aged 50 or above when their child is born is increasing, potentially affecting a growing number of children.

Advanced paternal age is becoming more common

The causes behind this shift are uncertain. Yet Albert Ha, a urologist at Stanford University, and his colleagues say it is frequently linked to "diminished concerns of the male 'biological clock' and the desire for educational and financial stability prior to starting a family."

"Previous studies have also highlighted the influence of evolving gender norms that promote active parental involvement while emphasizing traditional roles like the male 'breadwinner'," the authors add.

Because attention is generally focused firmly on mothers, the researchers are concerned that public understanding of the "modest but significant" risks linked with advanced paternal age (APA) remains limited.

A 2018 study examined many of the risks associated with later fatherhood, drawing on data for more than 40 million live births in the US between 2007 and 2016.

It found that babies with fathers older than 35 faced a greater likelihood of adverse outcomes, including low birth weight, seizures and breathing difficulties shortly after delivery.

The risk also rose with the father's age. For men aged 45 or over, their babies were 14 percent more likely to be born prematurely; for men aged 50 or above, their children had a 28 percent greater risk of admission to neonatal intensive care.

US births and the risks of mature fatherhood

Ha and colleagues assessed more than 46 million live births recorded in the US from 2011 to 2022. Their cross-sectional study shows that a larger proportion of US families may be exposed to these risks as more men choose to become parents at a later age.

Average paternal age increased consistently, from 30.8 years in 2011 to 32.1 years in 2022. Meanwhile, births to fathers aged 50 or over rose from 1.1 percent in 2011 to 1.3 percent in 2022-a modest but meaningful increase.

"Recent socioeconomic and demographic trends have shifted the timeline for family building in the US, with many couples increasingly delaying parenthood," Ha and colleagues write.

Even after accounting for maternal age and other variables, each additional 10 years of paternal age raised the proportion of births involving assisted reproductive technology (ART). Older paternal age was also connected with a greater chance that the birth was the mother's first, as well as higher risks of premature birth and low birth weight than among fathers aged 30 to 39.

How paternal age can affect fertility and child health

"Paternal age has also affected fertility, pregnancy trajectory, and child health," the authors write.

"Age-related conditions, such as erectile dysfunction and hypogonadism, impair paternal fecundity, while older age is associated with decreased semen volume, motility, and morphology."

Studies have also associated older paternal age with poorer sperm quality. This means sperm-the tiny, wriggling carriers of genetic material that provide half a baby's DNA-are more likely to be affected by DNA fragmentation, abnormal chromosome numbers, new mutations and epigenetic changes.

"Overall, the accumulation of alterations in older men may increase the risk of conditions like autism, pediatric cancers, achondroplasia, and schizophrenia; decrease likelihood of ART success; and heighten risk of perinatal complications," the authors write.

No meaningful differences in the infant sex ratio were identified according to paternal age, apart from among fathers aged 70 or over, who were more likely to have a female baby.

Overall, the findings point to a need for greater awareness of the risks linked to mature fatherhood and for further research into what is driving this social change.

The research is published in JAMA Network Open.