How old is too old to be a dad?

Mick Jagger just had his eighth kid at the age of 73. Is fathering a child later in life risky for your offspring?

There’s no expiration date on when guys can father a child. Case in point: Rocker Mick Jagger just had his eighth child at the age of 73.

Since men don’t hit menopause—the time in a woman’s life where her fertility ends—they can typically continue to father children into their later years.

And more and more men are choosing to do so.

But from 1980 to 2014, there has been a 58 percent increase in the number of guys 35 and older who brought home a new baby, according to the most recent government statistics.

In most cases, the increasing age is not really a cause for concern. The majority of these older dads don’t have fertility problems, and father babies without serious physical or developmental problems, says Robert E. Brannigan, M.D., a urologist and specialist in male reproductive medicine at Northwestern University’s Feinberg School of Medicine.

But that doesn’t mean delaying fatherhood is risk-free.

Aging Means Problems On Your Sperm Production LineWomen are born with all the eggs they’ll ever need. Men, on the other hand, are literal sperm factories.

You make about 1,000 swimmers every time your heart beats, says University of Washington endocrinologist Bradley Anawalt, M.D., a spokesperson for the Endocrine Society.

Most never fertilize an egg—they’re either released through ejaculation or broken down by the body once they’re past their prime.

But after you hit about age 30, some of your machinery starts to misfire, says Ranjith Ramasamy, M.D., director of male reproductive medicine and surgery at the University of Miami Miller School of Medicine.

You can blame exposure to things like radiation, environmental toxins, and plain old aging.

As you grow older and these factors  pile up, you lose both Leydig cells—the cells in your testicles that make testosterone—and Sertoli cells, which support and nurture new sperm, Dr. Brannigan notes.

As a result, your body starts to churn out more defective sperm, which contain DNA mutations that could harm your babies-to-be.

The average 30-year-old dad passes on about 55 mutations to his offspring, according to a paper published in Nature. But each year you age increases that number by two, the authors found.

That means every 16.5 years, the number of mutations you pass along will double. And in 50 years—say, at age 80 instead of 30—you’d bequeath eight times as many DNA mutations.

So How Risky Is Delaying Fatherhood, Really?Of course, not all these mutations cause health problems.

But some contribute to trouble conceiving or carrying a pregnancy to term, Dr. Ramasamy says.

For instance, one study from the U.K. found men age 35 and older had a 50 percent lower chance of conceiving after a year of trying than guys younger than 25 did.

Another study in the American Journal of Epidemiology found that women with partners age 35 and older were 27 percent more likely to experience a miscarriage than those with partners 25 or younger.

That link remains even after researchers factor in the effect of the mother’s age. This also boosts the chances of complications, since women’s eggs decline in number and quality over time.

Other mutations don’t affect conception or fetal development, but can cause birth defects, chromosomal abnormalities, or other genetic diseases in children, Dr. Ramasamy says.

In a Baylor College of Medicine review, the researchers crunched the numbers on 86 congenital problems linked to older fatherhood.

They concluded that the risk of having any of these issues increased from 1 in 50 among the general population to 1 in 42 among babies born to men age 40 and older.

Specifically, the risk of having a child with achondroplasia—a type of dwarfism—spikes from 1 in 15,000 to 1 in 1,923 once men reach age 50. And the risk of schizophrenia more than quadrupled, from 1 in 100 within the general population to 1 in 22 with fathers over 50.

What’s more, autism rates rise from 1 in 1,000 to 1 in 174 for kids whose dads had them after age 40.

Unfortunately, cancer rates among offspring also seem to rise too as their dads grow older, possibly because of some of the same DNA mutations that contribute to other conditions.

For example, a woman’s lifetime risk of breast cancer typically stands at 1 in 8, but rises to 1 in 5.3 if her dad was 40 or older when she was born, according to the same Baylor review.

And childhood leukemia strikes 1 in 36,000 kids in the general population, but 1 in 21,302 of those with fathers age 40-plus.

What’s an Older Dad to Do?The numbers seem scary, but it’s important to note that the majority of these older dads do father healthy children, says Dr. Brannigan.

In fact, it’s the mother’s age that plays an even bigger role on a baby’s health—that’s why women 35 and older receive more careful monitoring during pregnancy.

Doctors say there’s now an increasing recognition of dads’ contributions, but that there’s still more to learn.

It’s harder to study, because unlike moms, who are obviously present at birth, dads’ ages aren’t always recorded. So researchers don’t have as large a data set to pull from.

Plus, even researchers studying older dads don’t agree on what qualifies as “advanced paternal age,” Dr. Brannigan points out.

That means doctors who advise men about their reproductive health don’t have a standard age at which they raise red flags about these risks. What’s more, there’s no single test to assess the risk of having a child with these conditions.

Currently, doctors can screen your sperm for DNA mutations. But they must destroy them to do so, so you wouldn’t have any assurances that those results would match up with the next batch you produced, Dr. Ramasamy says.

And concerned couples can also go the in vitro fertilization (IVF) route, and use a technique called preimplantation genetic diagnosis, which tests each embryo for genetic diseases before it’s implanted into the woman’s womb.

But Dr. Ramasamy predicts that within the next five to 10 years, there will be a genetic test that can tell you if your sperm’s likely to cause problems.

If you’re older and want to father children, you can talk with a genetic counselor specifically trained in reproductive issues if you’re concerned, Dr. Brannigan says.