It is well established that a woman’s fertility declines with age. She is born with a finite supply of eggs, and her estrogen levels diminish as she approaches her menopausal years.

The effects of a man’s age, however, on procreation are not as well known. A man produces sperm throughout his life. Though not the norm, many men have fathered children into their fifties and sixties and beyond. John Stamos, George Clooney, and Mick Jagger are a few famous examples.

Though age does not have as dramatic an impact on men’s baby-making prowess, some factors could impede a man’s ability to father children.

Time to conceive

According to a study in the reproductive medicine journal Fertility and Sterility, researchers found that it took women longer to conceive when their male partners were 45 and older. For women 35 years of age and older, it took them five times as long as for those whose partners were 25 or younger. Among women 25 and younger, the time to pregnancy was four times longer if their male partner was 45 years or older.

Quality of sperm

Another Fertility and Sterility study reviewed published research literature that focused on the connection between male age, semen quality, fertility status, and pregnancy rates. Semen quality includes semen volume, concentration, motility, and morphology.

After excluding variables for female age, the stronger of the studies found that as men age there is a decline in all factors comprising semen quality except for sperm concentration.

Risk of miscarriage

The ages of prospective mothers and fathers both are risk factors for miscarriage. Several studies have demonstrated that older would-be dads raise the risk of miscarriage significantly from 25 to 50%. One study found a 60% increase in miscarriage probability if the father was over 40. Generally, the increase in miscarriages is more prevalent in the first trimester.

Risk of autism in children

One of the most serious consequences of advanced paternal age is an increased risk of autism in the children borne by older fathers. An analysis revealed that men aged 35 to 60 are up to 24 percent more likely to have children diagnosed with autism than children with fathers aged 31 to 34. Though its cause is not definitively known, autism may be attributed to spontaneous mutations in sperm that accumulate over time. Also, the risk increases steadily as a man ages.

IVF success

In vitro fertilization combined with Intracytoplasmic sperm injection, better known by its acronym ICSI, is responsible for the births of many children whose fathers experienced male factor infertility. However, older male partners lower IVF success rates.

In a large retrospective study of 19,000 IVF cycles, Harvard researchers found that live birth rates declined with the increasing age of the prospective father, though the age of the mother still was the primary factor determining success.

Age Matters

The age of hopeful fathers matters, but is not a crucial factor in determining fertility. A man continues to make a fresh supply of sperm approximately every 90 days. More research is needed to determine the impact of aging sperm on fertility, the development of chromosomal issues, and the health of future children conceived with sperm from a ‘mature’ man.