Study: Odds of Having a Boy or Girl Are Not Always 50-50

A new Harvard study suggests that biological factors, beyond chance, may influence the likelihood of having boys or girls in a family.

The research, which examined data from 58,000 women, found that mothers with three boys had a 61% chance of having a fourth boy, while mothers with three girls had a 58% chance of having a fourth girl.

Researchers speculate that the acidity level of the female vagina and genetic variations in chromosomes 10 and 18 may play a role.

The study notes that the mother's age may also affect the odds, as women who had their first child at age 29 or older were 13% more likely to give birth to only boys or girls.

However, the study has limitations, as the sample mainly included women of European descent.