Should Medicaid eligibility expansions be continued or extended? The answer depends on how these expansions have affected previously uninsured mothers and their children compared with their privately insured cohort. This study, conducted by Harvard University, evaluated the impact of the recent Medicaid eligibility expansions on a range of maternal and neonatal outcomes; changes in use, duration, and adequacy of prenatal care; incidence of Caesarian section; and length of hospital stay. The purpose of this planning grant was to identify states with large populations that have undergone a recent significant expansion in Medicaid coverage and that have hospital discharge and birth registry data available for research purposes. At the conclusion of the planning grant, California and South Carolina were selected for analysis.