- To evaluate the effect of the 2013-2014 ACA Medicaid Primary Care Rate Increase on Medicaid-insured women's prenatal care utilization, overall and by race and ethnicity.We employed a difference-in-differences design, using births data from the 2010-2014 National Vital Statistics System. Our study population included approximately 6.2 million births to Medicaid insured mothers conceived between April 2009 and March 2014. Our treatment group was births in states with large (relative to small) fee bump, defined as having Medicaid-to-Medicare fee ratio below the median of all states (0.7) in 2012. Our control group was births in states with a small fee bump. Prenatal care utilization measures included initiation of prenatal care in the first trimester and number of prenatal care visits.Non-Hispanic Black women giving births in large fee bump states had 9% higher odds (95% CI 1.02, 1.17) of initiating prenatal care in the first trimester during the fee bump period, compared to small fee bump states. Prenatal care visits in this group also increased by 0.24 (95% CI 0.10, 0.39), 2.4% of the mean. A smaller increase in prenatal care visits of 0.17 (95% CI 0.00, 0.33) was found among non-Hispanic Whites. The fee bump had no impact among Hispanics or non-Hispanic women of other races.The Medicaid "fee bump" improved prenatal care utilization for non-Hispanic Black and White women. Policymakers may consider reinstating higher Medicaid reimbursements to improve access to care for disadvantaged populations.