Social connectedness in the transition to parenthood: Implications for parent and child health and well-being - Project Summary One of the most important methods of promoting children’s positive adaptive skills is improving caregiver well- being6,7. Postpartum mood disorders affect up to 40% of new parents8-10, and confer significant risk to child development8,11. Additionally, the transition to parenthood triggers changes to social life, which may lead new parents—both mothers and fathers—to feel lonely and less socially connected3, which may exacerbate declines in parents’ mental health4,5. Social connectedness—the extent to which people feel close and connected to other people—is linked with improved mental and physical health across the lifespan12-14. Further, social connectedness is only moderately correlated with other relationship processes, such as social network size, relationship satisfaction, and social support15, suggesting that it may confer unique protective benefits. However, remarkably few studies have systematically investigated changes in social connectedness during the transition to parenthood and their implications for postpartum mental health and child development. Given the unique neurobiological, psychosocial, and behavioral changes that occur during the transition to parenthood16, research on social connectedness during the perinatal period and its connection to child development is needed. We propose to fill this critical knowledge gap in this R21 investigation. Specifically, we will examine social connectedness among first-time expectant mothers and fathers and their associations with health and well-being outcomes from pregnancy to 4-months postpartum. We will incorporate comprehensive measures of social connectedness (loneliness, connectedness), distress (depressive, anxiety, and birth-related PTSD symptoms), well-being (positive and negative emotion, life satisfaction), child development (delivery outcomes, Bayley Scales, temperament), and caregiving outcomes (parental sensitivity, parental bonding, parental reflective functioning). We propose that changes in social connectedness will be associated with parents’ postpartum distress and well-being, as well as child development and caregiving outcomes independent of other social processes. Furthermore, we propose that parents’ mental health will be one psychosocial mechanism linking social connectedness to child outcomes. The findings from this research will be important as they will demonstrate for the first time the unique transgenerational impact of mothers’ and fathers’ social connectedness, transforming understanding across multiple areas of research, including research on postpartum mental health, fatherhood, child development, and close relationships. Moreover, the successful completion of this research will establish an empirical foundation for additional investigations on biopsychosocial mechanisms linking social connectedness to health and well-being during the perinatal period, which will inform new intervention approaches targeting broader social connectedness. Given the importance of parent mental health for child development, improving parents’ experiences promises to benefit the entire family.