There is limited empirical evidence on whether cash transfers to poor pregnant women improve children's birth outcomes and potentially help weaken the cycle of intergenerational poverty. Using a unique array of program and social security administrative micro-data matched to longitudinal vital statistics in Uruguay, we estimate that participation in a generous social assistance program led to a sizable reduction in the incidence of low birthweight. The effect is due to faster intrauterine growth rather than longer gestational length. Our findings are consistent with improved maternal nutrition during pregnancy being a key driver of improved birthweight. (JEL I14, I32, I38, J13, J16, O15)