Despite the known benefits of breastfeeding to infants and mothers, previous studies have demonstrated that underserved women are less likely to exclusively breastfeed. Existing studies on the impact of Special Supplemental Nutritional Program for Women, Infants, and Children enrollment on feeding decisions for infants have conflicting results with low-quality data and metrics. This study aimed to examine infant feeding trends nationally in the first week postpartum over a 10-year period, comparing breastfeeding rates for primiparous women with low income who used Special Supplemental Nutritional Program for Women, Infants, and Children resources with those women who did not enroll. We hypothesized that although the Special Supplemental Nutritional Program for Women, Infants, and Children is an important resource for new mothers, free formula associated with enrollment in the Special Supplemental Nutritional Program for Women, Infants, and Children may disincentivize women to exclusively breastfeed. This was a retrospective cohort study of primiparous women with singleton gestations who gave birth at term and who responded to the Centers for Disease Control and Prevention Pregnancy Risk Assessment Monitoring System between 2009 and 2018. Data were extracted from phases 6, 7, and 8 of the survey. Women with low income were defined as those with a reported annual household income of $35,000 or less. The primary outcome was exclusive breastfeeding after 1 week postpartum. Secondary outcomes included ever breastfeeding, any breastfeeding after 1 week postpartum, and introduction of other liquids within 1 week postpartum. Multivariable logistic regression was used to refine risk estimates with adjustment for mode of delivery, household size, education level, insurance status, diabetes, hypertension, race, age, and BMI. Among the 42,778 women with low income who were identified, 29,289 (68%) of these women reported receiving Special Supplemental Nutritional Program for Women, Infants, and Children resources. There was no significant difference in the rates of exclusive breastfeeding after 1 week postpartum between those enrolled in the Special Supplemental Nutritional Program for Women, Infants, and Children and those not enrolled (adjusted risk ratio, 1.04; 95% confidence interval, 1.00-1.07; P=.10). However, those enrolled were less likely to ever breastfeed (adjusted risk ratio, 0.95; 95% confidence interval, 0.94-0.95; P<.01) and were more likely to introduce other liquids within 1 week postpartum (adjusted risk ratio, 1.16; 95% confidence interval, 1.11-1.21; P<.01). Although exclusive breastfeeding rates after 1 week postpartum were similar, women enrolled in the Special Supplemental Nutritional Program for Women, Infants, and Children were significantly less likely to ever breastfeed and more likely to introduce formula within the first week postpartum. This suggests that Special Supplemental Nutritional Program for Women, Infants, and Children enrollment may impact the decision to initiate breastfeeding and may represent an important window to test future interventions.