Why the Most Babies Are Born in the Summer

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Summer and early fall bring on a bumper crop of babies, most likely born on a Tuesday. Here’s why. (Photo: Corbis Images)

Early September is the time for end-of-summer barbecues, back-to-school shopping, and preseason NFL games.

And don’t forget newborns — lots of newborns. That’s because July and August are the most popular months of the year for births, according to data from the Centers for Disease Control and Prevention (CDC).

The numbers tell the story: Of about 3.9 million bundles of joy delivered every year in the United States, a little more than 353,000 make their way into the world in August, the biggest birthday month. The second most popular birth month is July, with about 349,000 deliveries.

And while September has vied for the top three spots over the years, in 2013, it came in fourth. October actually scored more births that year, the most recent year stats are available, according to the CDC.

Why do babies tend to appear in summer and early autumn? It may be that the sticky days of summer don’t lend themselves to romance the way the short, cold days of winter do.

“I’ve always noticed this seasonal birth pattern, and one thought is that people just have less sex in warmer months because it’s so hot out,” Mary Jane Minkin, MD, clinical professor of ob-gyn at Yale School of Medicine, tells Yahoo Parenting. That makes sense according to the data, which shows the fewest births in February, followed by April.

One evolutionary theory suggests that by making babies in the fall and winter, they’ll be born at a time of year when food is more available — and that gives offspring a better chance of surviving. This could explain why sperm tend to be healthier and stronger in the winter months, according to a 2013 study from the American Journal of Obstetrics and Gynecology.

As for the day of the week newborns make their grand entrances, CDC research from 2013 shows that Tuesday is most popular, with 12,323 births on average that day. Thursday and Wednesday are neck in neck for second and third place, with 12,064 and 12,037 births, respectively. Saturdays and Sundays in 2013 averaged 8,151 and 7,188 births per day, respectively.

“In our society, there are a fair number of inductions, and these generally get going in the early or the middle of the week,” says Minkin. Though C-sections certainly happen every day of the week, “elective C-sections are almost never scheduled for weekends,” she says.

And no matter what day a bambino comes into the world or whether it’s via a vaginal delivery or C-section, it’ll likely happen in the morning or midday hours, according to the CDC.

The exception to the Tuesday-is-most-popular rule: if it’s a major holiday. New Year’s Day, Fourth of July, and Christmas are the most unpopular birthdays, according to data culled from CDC stats spanning from 1994 to 2003.

The Christmas to New Year’s holiday season, however, is crucial in another respect: This is the time the most babies are conceived, based on a survey that suggests Oct. 5 is the most common birthday in the United States. If the average pregnancy lasts about 280 days, the date of conception for all of these Oct. 5 babies would be late December.

The least common birthday? May 22. So if you want your child to stand out and not have to share her special day with other kids, then September is your month to get busy.

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