Even if you have no plans to get pregnant in the near future, you probably have a sense of what you want. (Like a girl named Eva Charlotte or a boy named Evan Corey—but who's counting?)
While your baby's gender is determined at conception, there may be a new way to discover whether you're having a little Eva or Evan without any testing at all. And unlike old wives' tales about your baby bump's appearance and severity of morning sickness, this trick has lots of data to back it up:
In a massive new observational study published in PLOS ONE that accounts for more than 68 million births over 23 years, researchers found that women who gained the least weight during pregnancy were more likely to give birth to girls. Fifty-one percent of babies born to moms who gained less than 20 pounds during pregnancy ended up being girls.
Of course the study identifies a correlation, not a cause. So this doesn't mean that avoiding baby weight will guarantee you get a girl. (For the record, genetics and luck of the draw determine gender.) However, the amount of weight you gain during pregnancy could predict whether you've beaten the odds: Slightly more than 51 percent of all babies born (including those in this study) are boys.
Researchers still can't entirely explain the relationship between your weight gain and the likelihood that you'll give birth to a boy or girl. But they did find that mothers who gained low amounts of weight and miscarried were more likely to lose a male fetus than a female fetus.
One reason for this: Before birth, boys have higher metabolic rates than girls, which means they require more nutrients for growth and development. So they may be less likely to make it to full term in mothers who eat insufficient calories, according to researchers.
Again, the findings don't prove causation—they don't mean that you will lose your baby boy if you don't gain enough weight. The American Congress of Obstetricians and Gynecology recommends a 25- to 35-pound weight gain if you want a healthy baby—regardless of whether you want a girl or a boy.
This article originally appeared on Cosmopolitan.com. Minor edits have been made by the Cosmo.ph editors.