How (Not) to Predict a Baby's Sex, Round 2

Cristen Conger

This much girl baby cuteness? Scientifically unpredictable! (Victoria Blackie/Getty Images)

Just when we thought we had everything figured out about magically predicting how the sexual organs inside a fetus will turn out (barring telepathy -- although I could probably sell a TV series called "Mind Reading Mommies" faster than you can say 'breastfeeding'), some Japanese scientists had to come along and shake things right back up like a hysterical baby rattle.

A couple weeks ago, I posted about the tenuous correlation between maternal age and baby gender. In a nutshell, older parents supposedly have a higher chance of producing a girl child, while the young'uns make the boy babies.

Now, a Japanese study reported on by New Scientist links baby gender to menarche. Surveying 10,000 mothers about the age they experienced their first menstrual period (aka, menarche) and the sex of their children, the researchers concluded that the earlier Aunt Flo comes a-knockin', the likelier a woman is to have a girl. Women who had their first periods at age 10 had more girls than boys, whereas women who had their first periods at age 14 had more boys than girls.

The link might sound about as slim as the maternal age connection, but there's some valid science in there. From New Scientist: "Fukuda points to previous research demonstrating higher levels of the female sex hormone oestradiol in women who entered menarche before the age of 12. This may lead to spontaneous miscarriage of fertilised male eggs, he says."

At the same time, though, having slightly more girls isn't any sort of go-to baby gender predictor. Which is precisely why the world needs a reality show about a band of mystical, gender-envisioning doulas to save these scientists a lot of precious time and funding.

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