PROJECT SUMMARY In the United States, 45% of pregnancies are unintended and 35% of births are conceived within 18 months of a prior birth, the threshold used to define a short interpregnancy interval. Short interpregnancy intervals and unintended pregnancy are associated with adverse newborn health outcomes including preterm birth and low birthweight, and with pregnancy risk factors including gestational diabetes and obesity. A key determinant of safe birth spacing is use of an effective method of postpartum contraception. With failure rates of < 1%, immediate postpartum use of long acting reversible contraception (LARC) can facilitate safe interpregnancy intervals; however, fewer than 1% of women adopt these methods in the first month after delivery. Historically, widespread use of immediate postpartum LARC has been hindered by lack of provider reimbursement for inpatient LARC provision. In March 2012, South Carolina’s Medicaid program instituted a policy change allowing health care providers to bill Medicaid separately for LARC provided to women immediately postpartum in hospital settings. This study will evaluate the effect of Medicaid’s reimbursement policy change for inpatient LARCs in South Carolina on birth intervals and maternal and newborn health outcomes. As of 2016, the Medicaid programs of 14 states had changed their Medicaid policies to provide reimbursement for immediate postpartum LARC. This study will provide evidence on the effectiveness of the first of these policy changes initiated by the Medicaid program in South Carolina. Aim 1 will use Medicaid claims for labor and delivery between January 2008 and December 2018. We will create a variable equal to the monthly percentage women with a Medicaid funded delivery who had a short birth interval (defined as subsequent childbirth within 18 months). Using an interrupted time series model, we will analyze the impact of Medicaid’s immediate postpartum LARC reimbursement policy change on short birth intervals. Aim 2 will use the same Medicaid claims data described in Aim 1 linked to birth certificate data to obtain maternal and newborn health outcomes to analyze the impact of Medicaid’s immediate postpartum LARC reimbursement policy change on preterm and low birthweight using an interrupted time series regression model. Aim 3 Using the same analytic strategy and data source described in Aim 2, this analysis will analyze the impact of Medicaid’s immediate postpartum LARC reimbursement policy on maternal pre-pregnancy obesity and gestational diabetes using an interrupted time series regression model.