Northern New England states (Maine, New Hampshire, and Vermont) have among the highest rates of opioid dependence and other substance use conditions in the U.S. Our northern New England regions also have among the highest rates of newborns exposed to opioids through mothers with an opioid use disorder (OUD). Prenatal opioid use increases risk for poor infant outcomes, including preterm birth, pregnancy complications, and long hospitalization for newborns due to neonatal withdrawal. For pregnant women with OUD, medication assisted treatment (MAT) significantly improves outcomes. Many maternity care providers have begun to prescribe MAT in the context of prenatal care. Other providers have maintained what has been the standard of care, referring pregnant patients with OUD to specialty MAT treatment programs. Research is lacking to determine which model of providing MAT to pregnant women results in the best outcomes for women and their babies. Moms in Recovery (MORE): Defining Optimal Care for Pregnant Women and Infants is a 4-year, multisite observational comparative effectiveness study to identify the best models of MAT for pregnant women with OUD. Specifically, we are comparing maternal and infant outcomes for pregnant women with OUD receiving prenatal care in one of two setting types: 1) maternity care settings that offer MAT to pregnant women as part of their prenatal care, and 2) maternity care settings that refer pregnant women to specialty treatment for MAT.