When people talk about the “biological clock,” they usually refer to women and the age-related decline in egg reserves. However, male fertility also changes with age. Studies show that when couples experience difficulty conceiving, male and female factors occur at roughly equal rates, yet medical evaluations have traditionally begun with the woman. This approach is gradually changing. The World Health Organization (WHO) has emphasized the importance of assessing reproductive health regardless of sex, according to The Conversation.

From a biological perspective, sperm are produced continuously from puberty onward. However, beginning in the early twenties, the average number of sperm in ejaculate gradually starts to decline. In men older than 55, indicators often approach the threshold associated with infertility.

At the same time, fertility depends not only on sperm count. For successful conception, sperm must be viable, motile, and properly shaped. The volume of seminal fluid — which provides nutrition and transport — also plays an important role. From around the age of 30, the proportion of motile and morphologically normal sperm decreases, semen volume declines, and the number of nonviable cells increases. The most pronounced changes are typically observed after age 35.

These processes affect the likelihood of conception. In one study involving more than 2,000 couples, men over 45 took on average five times longer to achieve conception than men younger than 25. Another study showed that the probability of pregnancy within one year for 45-year-old men was 20% lower compared with peak fertility at age 30.

Genetic risks also increase with age. Spermatogonia — the precursor cells of sperm — divide hundreds of times throughout a man’s lifetime, and each division carries a risk of accumulating mutations. DNA and chromosomal damage may interfere with normal embryo development and increase the risk of miscarriage. In men over 40, the risk of pregnancy loss is approximately 30% higher than in men aged 25–29. The likelihood of chromosomal abnormalities associated with conditions such as Down syndrome or Klinefelter syndrome also rises.

Experts emphasize that most pregnancies proceed normally and most children are born healthy regardless of parental age. However, awareness of the male fertility factor allows couples to seek help sooner and choose an appropriate treatment strategy when necessary.