(Nature) – Families with three or more boys, for example, are more likely to have another boy than a girl as the next child.

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. (Read More)