A recent Harvard study has revealed that some families repeatedly having children of the same sex might not be a coincidence. Researchers analyzed birth records of 58,000 US nurses and found that in families with three or more children, the odds of continuing to have children of the same sex increased.

If a family has three boys, there is a 61% chance the next baby will also be a boy. For three girls, the chance of having a fourth girl is 58%.

This challenges the common belief that every pregnancy has an equal 50:50 chance. Researchers suggest age, body chemistry, and vaginal pH may influence which sperm (X or Y chromosome) fertilizes the egg.

Women who had their first child after 29 were also 13% more likely to have children of the same gender. However, data from fathers was missing in the study.

So, if you keep seeing families with four boys or four girls, it might actually be science-not just chance.