Fertility and mothers' labor supply: new evidence using time-to-conception

We analyze the impact of children on their mothers' labor market outcomes in the UK. We use time-to-conception of the first child as an exogenous variation in the probability of having more children. We find that having more children decreases the propensity to work in long part-time jobs but does not reduce participation for high- and intermediate-skilled mothers. For low skilled women, the impact on participation is large and negative. We show that the selection into having a second child is positive for for low-skilled mothers and negative for high-skilled and intermediate-skilled mothers. Women most attached to the labor market are also those that tend to have only one child among high- and intermediate-skilled women. The reverse is true for low-skilled women: those least attached to the labor market are also less likely to have a second child. This appears to be driven by unobserved attributes that negatively affect both labor market outcomes and the likelihood to remain in a relationship with the father of the first child, which in turn negatively affects the probability to have a second child.