When we talk about a biological clock ticking, it usually means the pressure women feel to fall pregnant before a certain age. It’s linked to the decline in eggs (ova) and fertility as females age.
But sperm numbers and fertility similarly decline with age in men. When a heterosexual couple experiences fertility issues, it’s equally likely due to male and female factors. Yet the woman is usually tested first.
But this is changing. New male infertility guidelines for Australian GPs recommend the male and female partner undergo investigations at the same time.
A growing body of research highlights the role of men in infertility and how a man’s age and health matters when trying to conceive. Let’s look at the evidence.
Semen and sperm health decline with age
Sperm are produced in the testes continuously from puberty, but sperm count (the average number of sperm in an ejaculate) starts to decline when a man is in his early twenties. Men over 55 have average sperm counts close to or below the threshold for infertility.
But it’s not just the number of sperm that matters.
Sperm need to be alive, have good motility (movement or “swimming ability”) and be the correct shape to reach and fertilise an egg in the female reproductive tract.
An adequate volume of semen (sperm and seminal fluid together) is also necessary because this provides nourishment to sperm.
Read more:
What’s the difference between sperm and semen? And can pre-ejaculate get you pregnant?
From around age 30, the number of sperm with good motility and correct shape, and semen volume decline, while the number of dead sperm increases. The biggest changes generally occur from around 35 years of age.
The age-dependent decline in sperm and semen affects male fertility. In studies of more than 2,000 couples, one study showed men older than 45 took five times longer to conceive than men younger than 25. Another study found the chance of falling pregnant within a year was 20% lower at 45 compared to the peak at 30.
Genetic damage and miscarriage risk increase with age
Though a sperm might have reached and fertilised an egg, if it contains genetic damage, this can also affect fertility or the baby.
As men age, their sperm accumulate more genetic damage, including damage to DNA and chromosomes (coils of DNA that carry genes). This is because sperm stem cells replicate hundreds of times during their life. Each time a cell replicates, there is a risk of genetic damage.
Genetic damage to sperm can stop the embryo developing and result in miscarriage. This is linked to about 30% higher chance of miscarriage in men older than 40 compared to those aged 25–29.
New techniques have shown chromosomal abnormalities in sperm also increase with age. These can cause birth defects and chromosomal syndromes such as Down syndrome and Klinefelter syndrome.