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Speaker 1: Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff.

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Speaker 1: Lauren vogelbamb here. It may seem as if you're buying

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Speaker 1: a lot more birthday gifts at certain times of the year,

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Speaker 1: But why is this? Is it your imagination or are

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Speaker 1: there really more babies born in specific months or on

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Speaker 1: specific days. If you look at births in the United

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Speaker 1: States from the twenty year period between nineteen ninety four

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Speaker 1: and twenty fourteen, a really clear pattern emerges. There were

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Speaker 1: an average of over six thousand to over twelve thousand

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Speaker 1: babies born on any given calendar day, but nine out

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Speaker 1: of the most ten common birthdays fell in September, with

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Speaker 1: the one outlier in July. A. September ninth was the

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Speaker 1: most common birthday during that time, with an average of

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Speaker 1: twelve thousand, three hundred and one berths on that day

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Speaker 1: every year. The rest of the dates range from September

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Speaker 1: ten through the twentieth, with September eleventh and the thirteenth

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Speaker 1: conspicuously missing. The July date is July seventh, But okay, why?

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Speaker 1: The short answer is that nobody knows for sure, and

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Speaker 1: it's a question that's veritably plagued researchers for over a century,

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Speaker 1: but there are some pretty credible hypotheses. First, a, people

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Speaker 1: may have extra free time and be feeling extra celebratory

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Speaker 1: during the year end holiday season, which happens to be

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Speaker 1: about nine months before all of those September birthdays. There

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Speaker 1: are a lot of parties going on, which often come

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Speaker 1: hand in hand with alcohol consumption, tending to lower inhibition

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Speaker 1: and increase sexual behavior. Plus, people usually have time off

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Speaker 1: from work over the holidays. A study is shown that

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Speaker 1: people have more sex on the weekends and over holiday periods,

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Speaker 1: and it's not just in the United States. A birth

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Speaker 1: seasonality has been observed around the world. One as yet

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Speaker 1: non pure reviewed study of data from a reproductive health

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Speaker 1: tracking app combined with birth records found that people's fertility

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Speaker 1: seems to peak right around the winter solstice in both

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Speaker 1: the northern and southern hemispheres. Interestingly, other studies have shown

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Speaker 1: that at higher latitudes that is further away from the equator,

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Speaker 1: where temperatures get colder earlier in the year, have fertility

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Speaker 1: rates that peak earlier closer to the autumn equinox. Closer

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Speaker 1: to the equator, where temperatures stay warmer longer, fertility rates

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Speaker 1: peak later, a closer to the spring equinox. There could

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Speaker 1: be multiple factors at work here, from caloric intake and

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Speaker 1: exercise strain during different seasons, to the sheer fact that

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Speaker 1: in the cold, dark months people spend less time outside,

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Speaker 1: leaving more time for indoor activities like canoodling. However, research

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Speaker 1: has shown that in the US, peaks in birth rates

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Speaker 1: across the calendar year have been evening out over the

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Speaker 1: past seventy years or so, a meaning that births are

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Speaker 1: less clustered around certain seasons. It's now more likely to

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Speaker 1: have a baby any day of the year. But within

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Speaker 1: that twenty year period from nineteen ninety four to twenty fourteen,

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Speaker 1: there were, of course least common birth dates. The very

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Speaker 1: least common was December twenty fifth, widely celebrated as Christmas Day.

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Speaker 1: On average, six five hundred and seventy four babies were

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Speaker 1: born each year on that day during the study period.

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Speaker 1: You can chalk this one up to the sheer number

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Speaker 1: of pre scheduled sea sections and inductions that we do

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Speaker 1: these days, and not too many doctors, midwives, or impending

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Speaker 1: parents really want to spend that holiday in the hospital

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Speaker 1: unless they don't have a choice. About it. I, for one,

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Speaker 1: really wrecked my parents' morial day plans when I showed

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Speaker 1: up a couple weeks early, though they said it was

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Speaker 1: worth it. The rest of the least common birthdays were

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Speaker 1: also centered around holidays Christmas Eve and the day after Christmas,

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Speaker 1: New Year's Day, and the day after July fourth, Halloween,

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Speaker 1: and right around Thanksgiving November twenty third, twenty fifth, and

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Speaker 1: twenty seventh. Even February twenty ninth, a date that only

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Speaker 1: comes around once every four years during leap years, was

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Speaker 1: still a more common birthday than any of these were,

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Speaker 1: with an average of over ten thoy four hundred births.

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Speaker 1: Perhaps parents aren't wary about that date for the reasons

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Speaker 1: that they may be wary about those others, or maybe

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Speaker 1: they enjoy the novelty cue lots of jokes about being

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Speaker 1: only seven years old on one's twenty eighth birthday, for example.

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Speaker 1: These changing trends show how much medical care has changed

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Speaker 1: in the past one hundred years, making people healthier year

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Speaker 1: round and giving us more options in when to be

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Speaker 1: pregnant and when and how to give birth. Today's episode

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Speaker 1: is based on the article what are the most and

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Speaker 1: least popular birthdays in the United States on HowStuffWorks dot

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Speaker 1: Com written by leoh Hoyt. Brain Stuff is production of

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Speaker 1: iHeartRadio in partnership with how Stuffworks dot Com and is

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Speaker 1: produced by Tyler Klang. Four more podcasts to my heart Radio,

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Speaker 1: visit the iHeartRadio app, Apple Podcasts, or wherever you listen

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Speaker 1: to your favorite shows.