NEED TO KNOW
- A new study challenges the long-held belief that a baby’s sex is randomly determined, finding that parents who already have multiples of one sex are more likely to have another child with that sex
- The study, published in the journal Science Advances, found that after age 28, mothers with three boys were 61% more likely to have another boy, and in families with three girls, they were 58% more likely to have another girl
- In a family with two or more children of one sex, the sex of another child is akin to “doing a coin toss with a two-headed coin”
Your baby’s sex may not be entirely up to chance, a new study says, challenging the long-held belief that parents have a 50-50 likelihood of giving birth to either a boy or a girl.
Previously, it was believed that “each fertilization event is random and independent, like a coin toss,” according to the study, which was published in the journal Science Advances. However, the research, which examined 146,000 pregnancies carried by 58,000 parents between 1956 and 2015, found that the likelihood of having a boy or a girl was heavily influenced by the sex of previous births — and that in multiple births, older mothers were more likely to have multiples of just one sex.
“If you’ve had two girls or three girls and you’re trying for a boy, you should know your odds are not 50-50,” the study’s senior author, Jorge Chavarro, told The Washington Post. “You’re more likely than not to have another girl.”
Specifically, the study found that in families with three boys, “the probability of having another boy was 61%.” Families with three girls were 58% more likely to have another girl.
Maternal age is also a factor, the study noted: “Older age at first birth was associated with higher odds of producing only males or only females,” the study found, with age 28 being the threshold.
The study’s authors acknowledged that the research was not without limitations. Ninety-five percent of the women studied were white women living in the United States, and researchers did not factor in any information provided by the fathers.
Still, the study found strong evidence that for some parents who are specifically trying to have a boy or girl, especially those who already have multiple daughters or sons, the cards might be stacked against them.
“Families desiring offspring of more than one sex who have already had two or three children of the same sex should be aware that when trying for their next one, they are probably doing a coin toss with a two-headed coin,” Chavarro told the Post.
Never miss a story — sign up for PEOPLE’s free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from celebrity news to compelling human interest stories.
Read the full article here