This study is part of the NIH’s Helping to End Addiction Long-term (HEAL) initiative to speed scientific solutions to the national opioid public health crisis. The NIH HEAL Initiative bolsters research across NIH to improve treatment for opioid misuse and addiction. This study will continue to build the evidence-basis for better treatment of opioid misuse and addiction in order to stem the national opioid public health crisis. The growing opioid-use epidemic in the U.S. has been associated with a significant increase in the prevalence of pregnant opioid-dependent women and neonatal abstinence syndrome, which is associated with adverse health effects for the infant and with costly hospitalizations. Maintenance with sublingual (SL) buprenorphine (BUP) is efficacious for opioid use disorder but has disadvantages that may be heightened in pregnant women including the potential for poor adherence, treatment dropout, and negative maternal/fetal effects associated with daily BUP peak-trough cycles. Extended release (XR) formulations may address some of these disadvantages. The objective of the NIDA CTN-0080 study, “Medication Treatment for Opioid Use Disorder in Expectant Mothers (MOMs)” (ClinicalTrials.gov Identifier: NCT03918850) is to evaluate the impact of treating opioid use disorder in pregnant women with BUP-XR, compared to BUP-SL, on maternal-infant outcomes. Testing a conceptual model of the mechanisms by which BUP-XR may improve maternal-infant outcomes, relative to BUP-SL, is a secondary trial objective.