- In the US, the UK, Italy and Sweden women whose first child is a boy work less than women with first-born girls. - Differently from the literature we show that after a first-born boy the probability that women have more children increases. - The positive impact on fertility of a first-born boy is one of the possible explanations of the lower labor supply of mothers. Women whose first child is a boy work less than women with first-born girls. After a first-born boy the probability that women have more children increases. Higher fertility is a possible explanation for the lower labor supply of mothers.