How to Conceive an Athlete

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circa 1945:  Studio portrait of an infant standing and holding a toy barbell over his head in a cloth diaper.  (Photo by Lambert/Getty Images)
Photo: Lambert/Getty Images

Many parents are obsessed with having their children be good at sports — YouTube is cluttered with videos of insane mothers screaming from the grandstands at high school football games and aggressive fathers pummeling referees who called one too many hand-checks on their kid. There’s a reason parents wake up at 4 a.m. to take their 5-year-olds to youth hockey leagues. But what if there were a way to channel that gusto and give your kid a leg up by simply partaking in a little bit of family planning?   

A new study published in the International Journal of Sports Medicine in November suggests there might be: simply conceive your kid during the second half of winter. Children conceived at this time of year, the research suggests, are more physically fit and stronger than peers born in other months.

The researchers, led by Dr. Gavin Sandercock, a clinical physiologist at the University of Essex, tested nearly 9,000 boys and girls between age 10 and 16 on tasks of strength, stamina, and cardiovascular fitness. Children born in October and November performed significantly better than the other kids. The study was designed, in part, to test whether birth month affects athleticism beyond the so-called relative age effect — given how age groupings are structured for youth sports leagues, kids born in certain months will enjoy a calendar-based advantage at certain junctures (more on this in a bit) — and it did, in fact, find an independent effect.

But why would your birth month, on its own, affect your athleticism? The researchers think it’s because the mothers of babies born in these months have greater exposure to Vitamin D as their due date draws near, thanks to those summer rays. Vitamin D has been linked to numerous in utero health benefits, and is thought to be a stimulus for bone and muscle growth, thus influencing the future athleticism of the unborn child. “With children born in the Northern Hemisphere, those born in autumn tend to have slightly bigger bone and muscle mass,” said Sandercock. “They start off with more muscle, become active earlier, then get involved in athletics sooner. It becomes a positive cycle.” (It’s safe to say, then, that in the southern hemisphere this biological advantage will be bestowed on kids born around April and May, while birth month probably matters less near the equator.)

In addition to biologically enhancing a child’s athleticism, getting pregnant in the spring can help ensure your kid is the biggest one on the team by taking advantage of the aforementioned relative age effect. This is a fancy name for the advantage children gain by being mere months older than their classmates owing to how age groupings are determined for youth leagues — an institutional bias that has been dissected in every form, from Canadian hockey players in Malcolm Gladwell’s Outliers to European soccer players in Steven Levitt and Stephen Dubner’s SuperFreakonomics.

For example, in the United States school begins in September — a centuries-old relic from the days when many children helped their families with the harvest — and most youth sports seasons coincide with the school year. So on a seventh-grade basketball team, the oldest members of the team would be born in September, October, and November, as players born earlier in the year would be members of the eighth-grade team. But those born the following April, six months later, would be on the same team as those born in September because they would still be in the seventh grade.

That’s a six-month gap, and at a young age a six-month gap can make a world of developmental difference. Those born in the fall will, all else being equal, be taller, stronger and faster, relative to their peers, and may hit puberty sooner. Because they are more physically mature, coaches are more likely to notice them, leading to more playing time and more overall attention — an advantage advantage researchers refer to as the Matthew Effect. These privileged kids then continue to improve their game beyond the skills of younger, underdeveloped teammates.

For a given kid born at the “right” time of year who ends up being a good athlete, it would be very hard to suss out how much of that is attributable to the biological effects revealed by Sandercock’s study, how much is attributable to the relative age effect, and how much is the big, murky category of “other stuff.” We can say with some certainty, though, that in studies of young soccer players, basketball players, and baseball players, kids born at this time of the year are, statistically speaking, over-represented in competitive leagues.

Once you get to the pros, however, it appears that things get so competitive that the early advantages of having the right birth month are washed out, so don’t expect your careful conception schedule to lead to a major-league contract (in fact, if you’re having pre-conception visions of your kid being a pro athlete, you might have some other stuff to work through).

There are other big factors, of course, that influence kids’ athletic development. Climate can have a profound effect. These statistical maps from Business Insider illustrate how a disproportionate number of professional athletes in the U.S. come from California, Texas and Florida. One might then conclude that warm weather benefits youth athletes because it allows for games and outdoor practice year-round. Culture can also have significant influence—as even the casual viewer of Friday Night Lights could tell you, in Texas, high school football is more religion than recreation, meaning talented young football players born there will enjoy certain inherent advantages that those born in less football-crazed places might miss out on.

Obviously, all these influences will only take you (or, more specifically, your kid) so far. Kevin Durant is not an NBA superstar just because he was born in September: Numerous other factors come into play—perhaps most importantly, genetics. If the average height in your family hovers around 5’5”, it’s unlikely your kid will be dunking anytime soon.

It’s clear, then, that success in sports comes from an amalgamation of elements, most of which are beyond a parent’s control. But given the crazy lengths so many parents will go to ensure their kids athletic success, and given how clear the benefits are to conceiving your (hopefully) athlete-to-be at the right time, it seems like a biological hack worth trying.

So, at the risk of mixing sports metaphors: This winter, the ball is in your court. Pull the proverbial goalie and swing for the reproductive fences.

Tyler Moss is a magazine writer and editor based in Cincinnati. Follow him on Twitter: @tjmoss11