Association of Revised WIC Food Package with Perinatal and Birth Outcomes: A Quasi-Experimental Study

Importance: The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) serves more than one-quarter of pregnant and postpartum women. In October 2009, the WIC food package underwent revisions to improve nutritional content. No studies have investigated the downstream effects of this revision on maternal and infant health. Objective: To investigate whether the revised WIC food package improved perinatal and birth outcomes among recipients. Design, Setting, and Participants: We conducted a quasi-experimental difference-in-differences analysis, comparing WIC recipients (the treatment group) before and after the package revisions while accounting for temporal trends among nonrecipients (the control group). Multivariable linear regressions were adjusted for sociodemographic covariates. This study was conducted using linked birth certificate and hospital discharge data from California from January 2007 to December 2012. Analysis began July 2018. Exposures: Whether pregnant women received the revised WIC package, which included more whole grains, fruit, vegetables, and low-fat milk. Main Outcomes and Measures: Measures of maternal and infant health, including maternal preeclampsia, gestational diabetes, and gestational weight gain as well as infant gestational age, birth weight, and hospitalizations. Results: The sample included 2897537 infants born to 2441658 mothers. WIC recipients were more likely to be Hispanic, less educated, of greater parity, and younger than nonrecipients. The revised WIC food package was associated with reductions in maternal preeclampsia (-0.6% points; 95% CI, -0.8 to -0.4) and more than recommended gestational weight gain (-3.2% points; 95% CI, -3.6 to -2.7), increased likelihood of as recommended (2.3% points; 95% CI, 1.8 to 2.8) and less than recommended (0.9% points; 95% CI, 0.5 to 1.2) gestational weight gain, and longer gestational age (0.2 weeks; 95% CI, 0.001 to 0.034). Among infants, an increased likelihood of birth weight that was appropriate for gestational age was observed (0.9% points; 95% CI, 0.5 to 1.3). Although birth weight itself was reduced (-0.009 SDs; 95% CI, -0.016 to -0.001), this was accompanied by reductions in small for gestational age (-0.4% points; 95% CI, -0.7 to -0.1), large for gestational age (-0.5% points; 95% CI, -0.8 to -0.2), and low-birth-weight infants (-0.2% points; 95% CI, -0.4 to -0.004), suggesting that the revised food package improved distributions of birth weight. Conclusions and Relevance: The revised WIC food package, intended to improve women's nutrition during pregnancy, was associated with beneficial impacts on maternal and child health. This suggests that WIC policy may be an important lever to reduce health disparities among high-risk women and children at a critical juncture in the life course.