ScienceIt Might Not Be As Simple as X and YWhat's going on: High school biology taught the masses that the odds of having a boy or a girl are supposed to be 50-50. However, that doesn’t explain how some families end up with six girls or four boys. One study looked into it. After analyzing data from more than 146,000 pregnancies, Harvard researchers found that a baby’s sex likely comes down to a “weighted coin toss” in families with at least three kids. That means if the first two children are girls, then it’s likely that their younger siblings will be too. Stats class didn’t prepare us for this one. What it means: Researchers think several factors could be at play. Statistically, women who give birth before the age of 23 have a 40% chance of having a same-sex family, compared to 50% for those 28 and older. Another potential factor: vaginal acidity (something else biology class left out). As women age, their menstrual cycles tend to shorten — which increases acidity and may affect whether X- or Y-carrying sperm survive. More research needs to be done. The study focused mostly on white women and didn’t account for the father’s role. But if this holds up, gender reveal parties might lose some of their allure. Related: Meanwhile, the US Fertility Rate Keeps Dropping (NBC) |