We use an exogenous variation in the Spanish legal working age to investigate the effect of education on fertility and infant health. The reform introduced in 1980 raised the minimum legal age to work from 14 to 16 years old. We show that the reform increased educational attainment, which led to 1786 more women remaining childless and 3307 less children being born in the 10 generations after the reform. These negative effects operate through a postponement of first births until an age where the catching up effect cannot take place. We show that woman's marriage market is one channel through which education impacts fertility, delaying the age at which women marry for the first time and reducing the likelihood that a woman marries. Even more importantly, this postponement in fertility seems to be also detrimental for the health of their offspring at the moment of delivery. The reform caused 2,789 more children to be born with less than 37 weeks of gestation, 268 died during the first 24 hours of life and 4,352 were born with low birth weight. We are able to document two channels that contribute to the negative effects on infant health: the postponement in age of delivery as well as a higher employment probability of more educated women, which enhances unhealthier behaviors (smoking and drinking).