ovaryI think most of us can recall that anxious time of waiting for our first period to arrive. We didn’t know exactly when it would happen–we just knew that one day it would leap out from behind a corner and surprise the heck out of us. And totally ruin our underwear.

I carried a pad around with me for years while waiting for my first drop of red, terrified I’d start menstruating someplace far from home and not have any menstrual aids nearby. Naturally, once I finally did get my period, my years-old pad had disintegrated at the bottom of my stylish Jordache purse, rendering it useless and forcing me to beg the school nurse for a menstrual pad hand-out.

I’m churning over these menstrual memories this morning because there’s an interesting new study that suggests the season when you’re born can impact when you get your first period.

Reporting in the American Journal of Human Biology, researchers who examined the birth dates and first-period dates of more than 1,600 females discovered that girls born in summer months (June, July and August) tend to start menstruating at a slightly younger age than those born at other times of the year. Among the girls studied, their periods arrived, on average, shortly before or after turning 13–a few months ahead of their peers.

Why the difference? While researchers aren’t sure, they point to certain environmental factors that women experience while pregnant that change with the seasons, such as how much vitamin D they get and melatonin they produce due to sun exposure, which types of produce are more readily available and how much air pollution there is–which may have an impact on fetal development.

While this information probably won’t help you determine when you get your first period (because, chances are, if you’re reading this Hormonology newsletter, you’ve had your period for awhile now), but it may shed a little light on why you got yours earlier or later than you friends or when your own daughter can expect hers.

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[Photo: Hey Paul Studios]