When it comes to fathering a child, time is not always on a man’s side.

More studies are showing that men, too, have biological clocks, and they may start ticking at around 40 years old, said the Department of Obstetrics and Gynaecology, KK Women’s and Children’s Hospital (KKH), a member of the SingHealth group. A recent study done in Singapore showed that advanced paternal age increased the risk of miscarriage.

The study monitored 139 women with threatened miscarriage (those with vaginal bleeding during early pregnancy) over a period of 16 weeks. It found that fathers over 40 years old added an eight-fold risk of miscarriage, compared to fathers between 30 and 40 years old.

For fathers between 30 and 40, the risk of miscarriage was about four times higher than fathers between 20 and 30 years old. The reason for the higher risk of miscarriage is linked to the decline in quality of sperm in older men. “Having noted an increased risk of foetal loss with a paternal age greater than 40, we can infer that the biological clock ticks not only in the woman, but also in the father-to-be."

The study, conducted jointly by KKH and Duke-NUS, contributes to the growing amount of evidence pointing to the fact that the age of the father affects not just fertility, but the health of the pregnancy and baby too. While research on the impact of women’s age on childbearing is well known, fewer studies have been done to determine the role that paternal age plays.

For women, their biological cut-off point is well defined at age 35. But for men, this could be at around 40 years old. “For a man above 40, we’ll be more worried that there could be a possibility of paternal DNA changes, and this can predispose his offspring to congenital problems or even lead to miscarriage."

How a man's clock ticks

Like women, men experience changes to their bodies and reproductive systems as they age, and this impacts their fertility and the health of their offspring.

While sperm production is unending in men, their production and transportation structures weaken over time, says the KKIVF Centre, KKH.

“For instance, the sperm production slows down and the reproductive tubes narrow. Beyond this, the prostate and urinary functions also change.”

The male sex function declines too. Over time, men’s testosterone levels dip, they experience a lower sex drive and are more susceptible to sexual problems like erectile dysfunction.

“Erectile dysfunction is closely linked to blood supply problems. When people get older, and if they have diabetes or high cholesterol levels, they are likely to have blood vessel problems. If such problems affect the penis, it leads to erectile dysfunction.”

In older men, sperm quality also becomes poorer. As sperm is produced at a slower rate, the risk of exposure to toxins through factors such as infection and smoking is higher. This can damage the DNA of the sperm. If the sperm’s DNA is more than 40 per cent damaged, there is a higher chance of miscarriage.

Studies have also shown that older fathers increase the risk of genetic problems such as autism and dwarfism in their children.

Read on to learn about factors affecting male fertility and advice from doctors.