The "Teen Mom Study: A Hybrid Cluster Randomized Trial" proposes a pragmatic, multilevel, type I study design to test the effectiveness of #BabyLetsMove - a 24-week mHealth and peer health coaching intervention paired with the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) - to increase physical activity and reduce sedentary behavior in pregnant, Black teens in the Mississippi Delta. Concurrently, a robust implementation evaluation will be conducted to determine feasibility and acceptability and to identify threats to organizational uptake, scalability, and sustainability. The intervention will be delivered remotely in partnership with WIC (Mississippi State Department of Health), the Telehealth Center of Excellence, and Myrlie Evers-Williams Institute (University of Mississippi Medical Center). The intervention is based on formative data from the "Teen Mom Study" and uses a theory-based, multi-level systems change approach. At the systems level, racially concordant young adult (18 to 25 years) WIC moms (n=4) are undergoing paid skills training in evidence-based peer health coaching to first, address social needs in pregnant teens and second, provide support for self-directed behavior change. At the individual level, pregnant, Black teens will be given three empirically supported behavior goals including (1) watching ≤2 hours of TV or other screen time per day, and (2) walking ≥10,000 steps per day - or - (3) engaging in ≥20 minutes of organized exercise per day. The intervention is designed to build social cognition, affect, and skills using four intervention components - a wearable tracker, interactive self-monitoring text messages with automated feedback, tailored skills training texts linked to digital materials, and peer health coaching. The central hypothesis is that augmenting usual WIC care with #BabyLetsMove will improve WIC's capacity to serve rural families and empower pregnant, Black teens to prioritize and improve their health. The primary aim is to determine the effect of #BabyLetsMove compared to usual WIC care on objective moderate-to-vigorous physical activity and sedentary behavior from ≤16 to 26- and 36-gestational weeks using a parallel cluster randomized trial. Secondary aim 1 will use wearables plus remote monitoring to measure and explore patterns of gestational weight gain and mean arterial pressure within/across conditions. Secondary aim 2.a. will use the RE-AIM framework to evaluate the feasibility and acceptability of #BabyLetsMove, and Secondary aim 2.b. will use the Practical, Robust Implementation and Sustainability Model and the Consolidated Framework for Implementation Research to identify threats to organizational uptake and to develop implementation strategies for future testing. This is believed to be the first digital health intervention study designed with/for a pregnant adolescent population. This study will add to our understanding of optimal mHealth and peer health coaching interventions; advance implementation science literature by studying a scalable and sustainable intervention in a novel setting; and contribute to the urgent national agenda to advance Black maternal health equity.