BackgroundThere is limited knowledge on the physiological and behavioral pathways that may affect the developmental outcomes of preterm infants and particularly on the link between autonomic nervous system maturation and early social human behavior. Thus, this study attempts to investigate the way heart rate variability (HRV) parameters are related to emotional coordination in interactions of preterm and full-term infants with their parents in the first year of life and the possible correlation with the developmental outcomes of infants at 18 months.ObjectiveThe first objective is to investigate the relationship between emotional coordination and HRV in dyadic full-term infant–parent (group 1) and preterm infant–parent (group 2) interactions during the first postpartum year. The second objective is to examine the relationship of emotional coordination and HRV in groups 1 and 2 in the first postpartum year with the developmental outcomes of infants at 18 months. The third objective is to investigate the effect of maternal and paternal postnatal depression on the relation between emotional coordination and HRV in the two groups and on developmental outcomes at 18 months. The fourth objective is to examine the effect of family cohesion and coping on the relation between emotional coordination and HRV in the two groups and on developmental outcomes at 18 months.MethodsThis is an observational, naturalistic, and longitudinal study applying a mixed method design that includes the following: (1) video recordings of mother-infant and father-infant interactions at the hospital, in the neonatal period, and at home at 2, 4, 6, 9, and 12 months of the infants’ life; (2) self-report questionnaires of parents on depressive symptoms, family cohesion, and dyadic coping of stress; (3) infants’ HRV parameters in the neonatal period and at each of the above age points during and after infant-parent video recordings; and (4) assessment of toddlers’ social and cognitive development at 18 months through an observational instrument.ResultsThe study protocol has been approved by the Research Ethics Committee of the University of Crete (number/date: 170/September 18, 2020). This work is supported by the Special Account for Research Funds of the University of Crete (grant number: 10792-668/08.02.2021). All mothers (with their partners) of full-term and preterm infants who give birth between March 2021 and January 2022 at the General University Hospital of Crete (northern Crete, Greece) will be invited to participate. The researcher will invite the parents of infants to participate in the study 1 to 2 days after birth. Data collection is expected to be completed by March 2023, and the first results will be published by the end of 2023.ConclusionsInvestigating the regulatory role of HRV and social reciprocity in preterm infants may have implications for both medicine and psychology.International Registered Report Identifier (IRRID)PRR1-10.2196/28089