Impact of the 2009 WIC revision on infant and maternal health: A quasi-experimental multi-state study.

Improving food security and dietary quality during pregnancy is vital for maternal and infant health. Poor nutrition can lead to adverse fetal development and complications for women. In 2009, the Special Supplemental Nutrition Program for Women, Infant, and Children (WIC), a US safety net program for low-income pregnant, breastfeeding or postpartum women and young children, was revised to improve dietary quality, promoting intake of whole grains, fruits, and vegetables. Prior studies found the revision improved dietary quality, but its impact on downstream health is less understood. We analyzed 2008-2012 national birth certificate data (N = 11,855,417) and employed a quasi-experimental difference-in-differences analysis to examine pre-post trends in outcomes among women predicted to be to be eligible for WIC (treatment group) while "differencing" out pre-post trends among predicted WIC-ineligible women (control group). Outcomes include infant birth weight and size for gestational age, and maternal gestational-diabetes-mellitus (GDM) and gestational-weight gain (GWG). The 2009 WIC revision was associated with small reductions in birth weight (-3.52 g; 95 %CI, -4.75 to -2.30) and small-for-gestational-age (-0.08 % points; 95 %CI, -0.15, -0.01), and GWG (-0.05 pounds; 95 %CI, -0.09, -0.02). While the results were robust to most sensitivity tests, they were not for some and therefore should be interpreted cautiously. Disparities emerged in the impact on GDM and GWG across subgroups. The limited evidence of positive effects on infant and maternal health underscores the need for ongoing research to better understand the impact of the 2019 WIC revision, including implementation factors and program design, on downstream health.