Within-Mother Estimates of the Effects of WIC on Birth Outcomes in New York City.

There is a large literature suggesting that "WIC works" to improve birth outcomes. However, methodological limitations related to selection into the WIC program have left room for doubt about this conclusion. This paper uses birth records from New York City to address some limitations of the previous literature. We estimate models with mother fixed effects to control for fixed characteristics of mothers and we directly investigate the way that time-varying characteristics of mothers affect selection into the WIC program. We find that WIC is associated with reductions in low birth weight, even among full term infants, and with reductions in the probability that a child is "small for dates." These improvements are associated with a reduction in the probability that the mother gained too little weight during pregnancy. Improvements tend to be largest for first born children. We also find that women on WIC are more likely to be diagnosed with chronic conditions, and receive more intensive medical services, a finding that may reflect improved access to medical care.