Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff. Lauren vogelbamb here. It may seem as if you're buying a lot more birthday gifts at certain times of the year, But why is this? Is it your imagination or are there really more babies born in specific months or on specific days. If you look at births in the United States from the twenty year period between nineteen ninety four
and twenty fourteen, a really clear pattern emerges. There were an average of over six thousand to over twelve thousand babies born on any given calendar day, but nine out of the most ten common birthdays fell in September, with the one outlier in July. A. September ninth was the most common birthday during that time, with an average of twelve thousand, three hundred and one berths on that day
every year. The rest of the dates range from September ten through the twentieth, with September eleventh and the thirteenth conspicuously missing. The July date is July seventh, But okay, why? The short answer is that nobody knows for sure, and it's a question that's veritably plagued researchers for over a century, but there are some pretty credible hypotheses. First, a, people may have extra free time and be feeling extra celebratory during the year end holiday season, which happens to be
about nine months before all of those September birthdays. There are a lot of parties going on, which often come hand in hand with alcohol consumption, tending to lower inhibition and increase sexual behavior. Plus, people usually have time off from work over the holidays. A study is shown that people have more sex on the weekends and over holiday periods, and it's not just in the United States. A birth
seasonality has been observed around the world. One as yet non pure reviewed study of data from a reproductive health tracking app combined with birth records found that people's fertility seems to peak right around the winter solstice in both the northern and southern hemispheres. Interestingly, other studies have shown that at higher latitudes that is further away from the equator, where temperatures get colder earlier in the year, have fertility
rates that peak earlier closer to the autumn equinox. Closer to the equator, where temperatures stay warmer longer, fertility rates peak later, a closer to the spring equinox. There could be multiple factors at work here, from caloric intake and exercise strain during different seasons, to the sheer fact that in the cold, dark months people spend less time outside,
leaving more time for indoor activities like canoodling. However, research has shown that in the US, peaks in birth rates across the calendar year have been evening out over the past seventy years or so, a meaning that births are less clustered around certain seasons. It's now more likely to have a baby any day of the year. But within that twenty year period from nineteen ninety four to twenty fourteen,
there were, of course least common birth dates. The very least common was December twenty fifth, widely celebrated as Christmas Day. On average, six five hundred and seventy four babies were born each year on that day during the study period. You can chalk this one up to the sheer number of pre scheduled sea sections and inductions that we do these days, and not too many doctors, midwives, or impending parents really want to spend that holiday in the hospital
unless they don't have a choice. About it. I, for one, really wrecked my parents' morial day plans when I showed up a couple weeks early, though they said it was worth it. The rest of the least common birthdays were also centered around holidays Christmas Eve and the day after Christmas, New Year's Day, and the day after July fourth, Halloween, and right around Thanksgiving November twenty third, twenty fifth, and
twenty seventh. Even February twenty ninth, a date that only comes around once every four years during leap years, was still a more common birthday than any of these were, with an average of over ten thoy four hundred births. Perhaps parents aren't wary about that date for the reasons that they may be wary about those others, or maybe they enjoy the novelty cue lots of jokes about being only seven years old on one's twenty eighth birthday, for example.
These changing trends show how much medical care has changed in the past one hundred years, making people healthier year round and giving us more options in when to be pregnant and when and how to give birth. Today's episode is based on the article what are the most and least popular birthdays in the United States on HowStuffWorks dot Com written by leoh Hoyt. Brain Stuff is production of iHeartRadio in partnership with how Stuffworks dot Com and is
produced by Tyler Klang. Four more podcasts to my heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.