In families with several children of the same sex, the odds of having another baby of that sex are higher than of having one of the opposite sex, according to a large study1 that investigated the maternal and genetic factors that influence the sex of offspring. The results, published in Science Advances today, find that in families with three boys, there is a 61% chance that the next sibling is male. For families with three girls, there was a 58% chance that the next child would be female. The findings challenge what people have been told about their baby's sex, which is that for each pregnancy, there is an equal chance of having either a boy or a girl, says Alex Polyakov, an obstetrician and researcher at the University of Melbourne, Australia. 'Based on these findings, you have to tell couples that their chance of having a different-sex child from what they already have is actually less than 50:50,' he says. Researchers at Harvard University in Boston, Massachusetts, looked at the...
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