Fertility, as it relates to advanced age, is becoming an increasingly hot topic as more couples defer having children into later stages of life. People are living longer, marrying later, and focusing on advancing their careers before considering having children. Advances in assisted reproductive technology (ART) have provided renewed hope to older parents who want to grow their family but are experiencing fertility issues.

A woman’s age has long been heralded as the primary factor affecting a couple’s ability to conceive, but is it true Father Time is always on Dad’s side? Does a man’s age affect his ability to produce offspring and are there any implications for the child? In short, does dad’s age matter?

Conventional wisdom has held men don’t have a biological clock when it comes to their sperm and producing offspring, but recent research is implying otherwise, especially when the health of the child is concerned. As men age, their sperm undergoes genetic mutations influencing fertility and also creating potential impacts on the physical and mental health of their future children.

At birth, women possess all the eggs they’re ever going to carry, up to two million strong. By puberty, the number has dwindled to no more than 400,000. A woman’s fertility begins to decline steadily at age 30, dipping rapidly after the age of thirty-seven. However, men continue to produce sperm well into middle age and older, providing a more gradual impact on a man’s infertility.

While there are no known caps to the age up until which males can produce offspring, there is currently a lack of understanding on the impacts of older paternal age on male fertility and the health of their progeny. One of the reasons for the confusion stems from the fact older men tend to have older partners, bringing the woman’s age into play while evaluating the results of any study. The key was to look at sample studies in older men with partners under 25-years-old or to adjust the study to reflect the age of the mother.

The conclusions of many studies show male fertility tends to begin its decline after the age of 40 when the production of testosterone starts to wane. Times to conception rise sharply after a man reaches 45 years and fertility doctors observed, after adjusting for maternal age, embryos produced by older men had considerably less chance of reaching the day five blastocyst stage. One study following donor egg cycles indicated a 5-year increase in paternal age resulted in a 26% decrease in the chances of a live birth.

The question remains then: when should a man be concerned his age may have an impact on his progeny’s health? The answer isn’t black and white largely because it is still uncommon for men to have children in their 50s and because there is still a lack of conclusive data on the subject.

A 2010 study out of Israel observed the offspring of men over forty had a five-fold risk of developing Autism Spectrum Disorder (ASD) compared to the general population. While the relative number may be disconcerting, given the rarity of ASD, what it means in absolute terms is roughly three in one thousand newborns.

One Swedish study of 14,000 patients discovered children born to men over 50-years-old developed bipolar disorder 37% more compared to the general population. Bipolar disorder is relatively uncommon in the United States with only 1% of the population diagnosed with the condition, putting the absolute risk level under 2%.

A second landmark study from Israel looked into the relationship between the older age of fathers and the development of schizophrenia among their adult children. The study concluded schizophrenia may be partially linked to genetic changes in a father’s sperm cells. The results displayed a gradual rise in progressive risk with a spike occurring after paternal age passed 50-years-old.

The pressures of having older parents to care for can put an emotional strain on a young person attempting to make their mark in society, a factor compounded by men who father children after the age of fifty. Conventional wisdom dictates younger adults who lose a parent earlier on in life may be more susceptible to depression and require mental health intervention.

Although recent individual studies support the link between the genetic mutations in the sperm of older men and the increased risk of mental disorders among their children, experts remain uncertain if age is the leading cause of these problems, given the vast majority of the illnesses are very rare.

At the end of the day, in a society having placed the utmost importance on maternal age, it has been confirmed a father’s age matters too. This paradigm shift means both mom and dad will now need to check their ticking biological clocks.