A study from Harvard examined the birthing records of over 58,000 women from the Nurses' Health Study, covering nearly 150,000 pregnancies from 1956 to 2015. Findings revealed that families having three or more children were more likely to have all boys or all girls instead of the expected 50/50 chance. The researchers found that offspring sex followed a beta-binomial distribution, indicating unique probabilities for each family. Specifically, families with three boys had a 61% chance of another boy, while families with three girls had a 58% chance of another girl. Older maternal age also correlated with these single-sex outcomes.
Researchers analyzed the birthing records of over 58,000 women from the Nurses' Health Study spanning nearly 150,000 pregnancies from 1956 to 2015.
The study discovered that families with three or more children had a higher likelihood of having all boys or all girls, contradicting the expected 50/50 odds.
Offspring sex followed a beta-binomial distribution, suggesting that each family has a unique probability of male or female births, like a weighted coin toss.
The findings indicate that having three boys increases the probability of the next child being a boy to 61%, while having three girls raises the odds to 58%.
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