Fathers' oxytocin responses to first holding their newborns: Interactions with testosterone reactivity to predict later parenting behavior and father-infant bonds.

Little is known about human fathers' physiology near infants' births. This may represent a period during which paternal psychobiological axes are sensitive to fathers' new experiences of interacting with their newborns and that can provide insights on how individual differences in fathers' biology relate to post-partum parenting. Drawing on a sample of men in South Bend, IN (U.S.), we report results from a longitudinal study of fathers' oxytocin, cortisol, and testosterone (N = 211) responses to their first holding of their infants on the day of birth and men's reported caregiving and father-infant bonding at 2-4 months post-partum (N = 114). First-time fathers' oxytocin was higher following first holding of their newborns, compared to their pre-holding levels. Contrasting with prior results, fathers' percentage change in oxytocin did not differ based on skin-to-skin or standard holding. Drawing on psychobiological frameworks, we modeled the interactions for oxytocin reactivity with testosterone and cortisol reactivity, respectively, in predicting father-infant outcomes months later. We found significant cross-over interactions for (oxytocin × testosterone) in predicting fathers' later post-partum involvement and bonding. Specifically, we found that fathers whose testosterone declined during holding reported greater post-partum play if their oxytocin increased, compared to fathers who experienced increases in both hormones. We also observed a similar non-significant interaction for (oxytocin × cortisol) in predicting fathers' post-partum play. Fathers whose testosterone declined during holding also reported less involvement in direct caregiving and lower father-infant bonding if their oxytocin decreased but greater direct care and bonding if their testosterone increased and oxytocin decreased. The results inform our understanding of the developmental time course of men's physiological responsiveness to father-infant interaction and its relevance to later fathering behavior and family relationships.