Reassessing the Association between WIC and Birth Outcomes Using a Fetuses-at-Risk Approach
Objectives Women with longer, healthier pregnancies have more time to enroll in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC), biasing associations between WIC and birth outcomes. We examined the association between WIC and preterm birth (PTB), low birth weight (LBW), and perinatal death (PND) using a fetuses-at-risk approach to address this bias, termed gestational age bias. Methods We linked California Medi-Cal recipients with a singleton live birth or fetal death from the 2010 Birth Cohort to WIC participant data (n = 236,564). We implemented a fetuses-at-risk approach using survival analysis, which compared, in each week of gestation, women whose pregnancies reached the same length and who had the same opportunity to utilize WIC. In each gestational week, we assessed WIC enrollment and the number of food packages redeemed thus far and computed hazard ratios (HR) using survival models with time-varying exposures and effects. Results Adjusting for maternal socio-demographic and health characteristics, WIC enrollment was associated with a lower risk of PTB from week 29–36 (HR29 = 0.71; HR36 = 0.52); LBW from week 26–40 (HR26 = 0.77; HR40 = 0.64); and PND from week 29–43 (HR29 = 0.78; HR43 = 0.69) (p < 0.05). The number of food packages redeemed was associated with a lower risk of PTB from week 27–36 (HR27 = 0.90; HR36 = 0.84); LBW from week 25–42 (HR25 = 0.93; HR42 = 0.88); and PND from week 27–46 (HR27 = 0.94; HR46 = 0.91) (p < 0.05). Conclusions for Practice To our knowledge this is the first study to examine the association between WIC and birth outcomes using this approach. We found that beginning from about 29 weeks, WIC enrollment was associated with a reduced risk of PTB by 29–48 %, LBW by 23–36 %, and PND by 22–31 %.
KeywordsWIC Birth outcomes Gestational age bias Survival analysis Fetuses-at-risk
This work was supported by funds from the California Title V Maternal and Child Health Services Block Grant; and the California Special Supplemental Nutritional Program for Women, Infants and Children (WIC).
This work began while Dr. Fingar was employed at the Maternal, Child and Adolescent Health Program, Department of Public Health, Sacramento, CA. Dr. Fingar designed the study and directed its implementation, analyzed the data, conducted the literature review, and drafted and revised the manuscript. This work began while Dr. Lob was employed at the Maternal, Child and Adolescent Health Program, Department of Public Health, Sacramento, CA. Dr. Lob participated in the analysis of data, development of methods, literature review, and drafted and revised the manuscript. Dr. Dove participated in the analysis of data, development of methods, and drafted and revised the manuscript. Dr. Gradziel participated in the acquisition and interpretation of data and drafted and revised the manuscript. Dr. Curtis contributed to the conception and design of the study; oversaw the acquisition, analysis, and interpretation of data; and drafted and revised the manuscript.
Compliance with Ethical Standards
Conflicts of Interest
There may be the appearance of a conflict of interest as this project was comprised of staff funded by California Title V Maternal and Child Health Services Block Grant and Special Supplemental Nutritional Program for Women, Infants and Children funds.
- Bell, L. (2004). Linking WIC program data to Medicaid and Vital Records Data Phase II Report, Data development initiatives for research on Food Assistance and Nutrition Programs—Final Report. Retrieved from http://www.ers.usda.gov/publications/efan-electronic-publications-from-the-food-assistance-nutrition-research-program/efan04005-2.aspx#.U0WRKFfMf-A.
- Devaney, B., Schirm, A. (1993). Infant mortality among medicaid newborns in Five States: The effects of prenatal WIC participation. Retrieved from http://www.fns.usda.gov/sites/default/files/InfMort-Pt1.pdf. (Published May 1993).
- Greenland, S. (2003). Quantifying biases in causal models: Classical confounding vs. collider-stratification bias. Epidemiology (Cambridge, Mass.), 14(3), 300–306.Google Scholar
- Kowaleski-Jones, L., & Duncan, G. J. (2002). Effects of participation in the WIC program on birthweight: Evidence from the National Longitudinal Survey of Youth. Special Supplemental Nutrition Program for Women, Infants, and Children. American Journal of Public Health, 92(5), 799–804.CrossRefPubMedPubMedCentralGoogle Scholar
- Kuklina, E. V., Whiteman, M. K., Hillis, S. D., Jamieson, D. J., Meikle, S. F., Posner, S. F., & Marchbanks, P. A. (2008). An enhanced method for identifying obstetric deliveries: Implications for estimating maternal morbidity. Maternal and Child Health Journal, 12(4), 469–477.CrossRefPubMedGoogle Scholar
- Lu, M., & Lu, J. (2007). Maternal nutrition and infant mortality in the context of relationality: The courage to love: Infant Mortality Commission Implications for Care, Research, and Public Policy to reduce infant mortality rates. Retrieved from http://www.asphn.org/resource_files/458/458_resource_file2.pdf.
- Mitchell, E. M., Hinkle, S. N., & Schisterman, E. F. (2016). Its about time, a survival approach to gestational weight gain and preterm delivery. Epidemiology (Cambridge, Mass.), 2, 182–187.Google Scholar
- Oliveira, V.J., Racine, E., Olmsted, J., & Ghelfi, L.M. (2002). The WIC Program: Background, trends, and issues. Retrieved from http://www.ers.usda.gov/publications/fanrr-food-assistance-nutrition-research-program/fanrr27.aspx#.U0WhdFfMf-A.
- Platt, R. W., Joseph, K. S., Ananth, C. V., Grondines, J., Abrahamowicz, M., & Kramer, M. S. (2004). A proportional hazards model with time-dependent covariates and time-varying effects for analysis of fetal and infant death. American Journal of Epidemiology, 160(3), 199–206.CrossRefPubMedGoogle Scholar
- Sonchak, L. (2016). The impact of WIC on birth outcomes: New evidence from South Carolina. Maternal and Child Health Journal. Retrieved from http://link.springer.com/journal/10995/onlineFirst/page/1.
- United States Department of Agriculture, Food and Nutrition Service. (2013). WIC Program: Total participation. Retrieved from http://www.fns.usda.gov/pd/27wilatest.htm.
- Villar, J., Merialdi, M., Gulmezoglu, A. M., Abalos, E., Carroli, G., Kulier, R., & de Onis, M. (2003). Nutritional interventions during pregnancy for the prevention or treatment of maternal morbidity and preterm delivery: an overview of randomized controlled trials. The Journal of Nutrition, 133(5 Suppl 2), 1606S–1625S.PubMedGoogle Scholar