Fertility and maternal labor supply in Japan: Conflicting policy goals?

Using panel data on Japanese mothers, this paper estimates the impact of fertility on maternal labor supply using twins as an instrument for the total number of children. We find that having twins actually has a longer term positive impact on maternal labor force participation in Japan. To understand this result, we present evidence that the effects of age and cost of children can generate this finding, are particularly salient in Japan and differ in important ways between twins and non-twin families of the same size. Implications for fertility and labor supply policy in Japan are discussed.