The Patient Protection and Affordable Care Act (ACA) required new private insurance plans to provide breast pumps with no cost sharing beginning August 2012, and in January 2014 expanded this requirement to Marketplace plans and expanded Medicaid coverage. We first examined the associations between the ACA reforms in 2012 and 2014 with rates of breast pump claims between Medicaid enrollees and those with private insurance. We next examined the associations between the monthly rate of breast pump claims with breastfeeding initiation and duration by insurance type. Using 2011-2015 public and private health insurance claims in All-Payer Claims Databases from Massachusetts, Maine, and New Hampshire, we conducted a linear regression model to evaluate the associations between the 2012 and 2014 ACA health insurance reforms with rates of breast pump claims by health insurance status. We then linked the monthly rates of breast pump claims per 1,000 live births to the Pregnancy Risk Assessment Monitoring System with self-reported breastfeeding initiation and duration. We estimated probit regression models to examine the associations between monthly rates of breast pump claims per state, insurance type, age group, and breastfeeding outcomes. For the 2012 ACA reform, breast pump claims increased by 183.4 (143.7-223.1) per 1,000 live births for women with private insurance, but decreased for Medicaid enrollees (-99.3 [-139.0 to -59.6]). For the 2014 ACA reforms, the opening of health insurance Marketplaces had no effect on breast pump claims for women with private insurance (8.3 [-43.6 to 60.2]), whereas Medicaid expansion increased claims by 119.4 (67.5-171.3) per 1,000 live births for Medicaid enrollees. Every additional 10 breast pump claims per 1,000 live births was associated with a 1.08 percentage point increase in breastfeeding initiation among women with private insurance (0.108 [0.018-0.198]), but not Medicaid enrollees (0.076 [-0.078 to 0.230]). In contrast, every additional 10 breast pump claims per 1,000 live births was associated with a 1.79 percentage point increase in breastfeeding for 4 or more weeks for women with private insurance (0.179 [0.063-0.294]) and a 2.05 percentage point increase among women with public insurance (0.205 [0.033-0.376]). Interaction analysis revealed no significant differences in associations by insurance type across breastfeeding outcomes. The ACA breastfeeding coverage requirements fill a gap for women wanting to obtain a breast pump to support breastfeeding. The monthly rate of breast pump claims, as an indicator of access, translated into higher levels of breastfeeding for women with private and public insurance with the potential to reduce socioeconomic disparities.