BACKGROUND:Prevention of mother-to-child transmission of HIV implementation faces significant challenges globally, particularly in the context of universal lifelong antiretroviral therapy (ART) for all HIV-infected pregnant women. METHODS:We describe the rationale and methods of the Maternal and Child Health-Antiretroviral Therapy (MCH-ART) study, an implementation science project examining strategies for providing HIV care and treatment to HIV-infected women who initiate ART during pregnancy and their HIV-exposed infants. RESULTS:MCH-ART is composed of 3 interrelated study designs across the antenatal and postnatal periods. Phase 1 is a cross-sectional evaluation of consecutive HIV-infected pregnant women seeking antenatal care; phase 2 is an observational cohort of all women from phase 1 who are eligible for initiation of ART following local guidelines; and phase 3 is a randomized trial of strategies for delivering ART to breastfeeding women from phase 2 during the postpartum period. During each phase, a set of study measurement visits is carried out separately from antenatal care and ART services; a maximum of 9 visits takes place from the beginning of antenatal care through 12 months postpartum. In parallel, in-depth interviews are used to examine issues of ART adherence and retention qualitatively, and costs and cost-effectiveness of models of care are examined. Separate substudies examine health outcomes in HIV-uninfected women and their HIV-unexposed infants, and the role of the adherence club model for long-term adherence and retention. DISCUSSION:Combining observational and experimental components, the MCH-ART study presents a novel approach to understand and optimize ART delivery for MCH.