Becoming a parent marks a critical life transition that introduces unique stressors and challenges. Stress during pregnancy can affect both parents’ health and their baby’s development. Many families across the United States turn to grandparents for emotional support and practical help during pregnancy and after the baby arrives, but the impact of these extended family supports is not well understood. This project examines the impact of grandparental support on prenatal stress and infant socioemotional outcomes. Broader impacts of this project include wide dissemination of the research findings to improve the public’s understanding of science and the scientific method. This project uses a longitudinal, multi-method design to examine how grandparental involvement during the transition to parenthood impacts prenatal stress mechanisms and subsequent infant socioemotional development. This project aims to (1) characterize patterns of grandparental involvement during pregnancy and postpartum through interviews and surveys; (2) investigate how grandparental involvement relates to psychological distress, physiological stress recovery, and inflammation during pregnancy; and (3) assess downstream effects on infant emotion and stress regulation at 3, 6, and 12 months of age. The project integrates psychological, biological, and observational methods (including heart rate variability during stress tasks, inflammatory biomarkers, and behavioral coding of mother-infant interactions) to