Delaying fatherhood has its costs. Despite largely being able to reproduce until death, male fertility may take a hit with age and could pose some serious developmental risks to newborn babies, several studies show.

It's not just women who should be concerned about their biological clocks: Typically the conversation about fertility has focused on female fertility and how putting off motherhood can potentially make pregnancy harder and increase the likelihood of congenital diseases in newborns. This focus — which stems from the fact that women have a fixed egg count from birth, while males can continually produce sperm as long as they’re alive — has traditionally eclipsed the very serious implications that may occur from being an older father.

Men are having children later in life than they used to: Since the 1970s, the number of fathers in the US under 30 has gone down by more than 27%, while the number of new fathers between 45-49 has ballooned by some 52%, according to a study conducted in 2017.It’s a phenomenon that we witness around the globe from Egypt to China, and from Germany to Japan.

Sperm count and quality declines as men age: Several studies have shown that age can be a significant determinant in sperm quality. As men get older their sperm count drops, gets slower and a higher percentage is considered damaged or has undergone mutation — potentially making it more challenging to conceive a child.But even when a couple manages to successfully conceive, the chances that the pregnancy ends in miscarriage or stillbirth arehigher for women with older partners.

The risk of physical birth defects grows over time, as well: Similar to women, older fathers are more likely to see babies with congenital abnormalities like cleft lip, a hole in the diaphragm, and even some cancers. The chances of childhood leukemia for example increases by 13% for every five years older the father is, according to this 2017 study in Denmark.

The neurological consequences can be serious, too: Kids born to fathers over 40 are nearly six times more likely to have autism than those whose fathers were younger than 30, researchers have found. The risk of children born to men over 50 developing schizophrenia also goes up by 89%.

But it’s not all doom and gloom: Some researchers suggest that the potential health risks to newborn babies posed by delayed fatherhood can be somewhat staved off by the egg of a younger partner. While these factors are important to consider if you’re deciding whether to have children later in life, it’s not the end all be all. Other environmental factors like stress, health, and socioeconomic conditions — which some researchers argue are even stronger determinants of newborn health — should also come into play.

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