Men have a biological clock too. Here’s what’s more likely when dads are over 50

By Karin Hammarberg for The Conversation

Wellington: We hear a lot about women’s biological clock and how age affects the chance of pregnancy.

New research shows men’s fertility is also affected by age. When dads are over 50, the risk of pregnancy complications increases.

Data from more than 46 million births in the United States between 2011 and 2022 compared fathers in their 30s with fathers in their 50s.

While taking into account the age of the mother and other factors known to affect pregnancy outcomes, the researchers found every ten-year increase in paternal age was linked to more complications.

The researchers found that compared to couples where the father was aged 30–39, for couples where the dad was in his 50s, there was a: 16 per cent increased risk of preterm birth 14 per cent increased risk of low birth weight 13 per cent increase in gestational diabetes.

The older fathers were also twice as likely to have used assisted reproductive technology, including IVF, to conceive than their younger counterparts.

Dads are getting older

In this US study, the mean age of all fathers increased from 30.8 years in 2011 to 32.1 years in 2022.

In that same period, the proportion of men aged 50 years or older fathering a child increased from 1.1 per cent to 1.3 per cent.

We don’t know the proportion of men over 50 years who father children in Australia, but data shows the average age of fathers has increased.

In 1975 the median age of Australian dads was 28.6 years. This jumped to 33.7 years in 2022.

How male age affects getting pregnant

As we know from media reports of celebrity dads, men produce sperm from puberty throughout life and can father children well into old age.

However, there is a noticeable decline in sperm quality from about age 40.

Female partners of older men take longer to achieve pregnancy than those with younger partners.

A study of the effect of male age on time to pregnancy showed women with male partners aged 45 or older were almost five times more likely to take more than a year to conceive compared to those with partners aged 25 or under. More than three quarters (76.8 per cent) of men under the age of 25 years impregnated their female partners within six months, compared with just over half (52.9 per cent) of men over the age of 45.

Pooled data from ten studies showed that partners of older men are also more likely to experience miscarriage. Compared to couples where the male was aged 25 to 29 years, paternal age over 45 years increased the risk of miscarriage by 43 per cent.

Older men are more likely to need IVF

Outcomes of assisted reproductive technology, such as IVF, are also influenced by the age of the male partner.

A review of studies in couples using assisted reproductive technologies found paternal age under 40 years reduced the risk of miscarriage by about 25 per cent compared to couples with men aged over 40.

Having a male under 40 years also almost doubled the chance of a live birth per treatment cycle. With a man over 40, 17.6 per cent of treatment rounds resulted in a live birth, compared to 28.4 per cent when the male was under 40.

How does male age affect the health outcomes of children?

As a result of age-related changes in sperm DNA, the children of older fathers have increased risk of a number of conditions. Autism, schizophrenia, bipolar disorders and leukaemia have been linked to the father’s advanced years.

A review of studies assessing the impact of advanced paternal age reported that children of older fathers have increased rates of psychiatric disease and behavioural impairments.

But while the increased risk of adverse health outcomes linked to older paternal age is real, the magnitude of the effect is modest. It’s important to remember that an increase in a very small risk is still a small risk and most children of older fathers are born healthy and develop well.

Improving your health can improve your fertility In addition to the effects of older age, some chronic conditions that affect fertility and reproductive outcomes become more common as men get older. They include obesity and diabetes which affect sperm quality by lowering testosterone levels.

While we can’t change our age, some lifestyle factors that increase the risk of pregnancy complications and reduce fertility, can be tackled. They include: smoking recreational drug taking anabolic steroid use heavy alcohol consumption.

Get the facts about the male biological clock Research shows men want children as much as women do. And most men want at least two children.

Yet most men lack knowledge about the limitations of female and male fertility and overestimate the chance of getting pregnant, with and without assisted reproductive technologies.

We need better public education, starting at school, to improve awareness of the impact of male and female age on reproductive outcomes and help people have healthy babies.

For men wanting to improve their chance of conceiving, the government-funded sites Healthy Male and Your Fertility are a good place to start. These offer evidence-based and accessible information about reproductive health, and tips to improve your reproductive health and give your children the best start in life.

(Karin Hammarberg Karin Hammarberg is a friend of The Conversation and a Senior Research Fellow, Global and Women's Health, School of Public Health & Preventive Medicine, Monash University.)