Background: During the last decades, the research on mother-infant dyad has produced a great amount of data, methods and theories, which largely contributed to set a revolution in the way we look at developmental changes during infancy and childhood. Very different constructs depict the different aspects of the “dyadic dance” occurring between a mother and her infant; nonetheless, a comprehensive and consistent systematization of these concepts in a coherent theoretical landscape is still lacking. Aim: In the present work, we aim at disentangling the different theoretical and methodological definitions of 9 dyadic constructs and we highlight their effects on infants' and children developmental outcomes. Methods: A literature search has been conducted on three databases—PubMed, Scopus, Web of Science. Three different reviews are reported here: (1) a review on the theoretical definitions of dyadic constructs; (2) a review of operational definitions, settings and methods of dyadic processes; (3) a systematic review of dyadic processes' outcomes for infants' and children developmental trajectories. Results: Two constructs emerged as wide meta-theoretical concepts (reciprocity and mutuality) and seven described specific processes (attunement, contingency, coordination, matching, mirroring, reparation, synchrony). A global model resuming the relationships among different processes is reported, which highlights the emergence of two specific cycles of dyadic functioning (i.e., matching-mismatching-reparation-synchrony; contingency, coordination, attunement, mirroring). A comprehensive review of the adopted measures is also provided. Finally, all the processes provided significant contributions to infants' behavioral, cognitive, and socio-emotional development during the first 3 years of age, but limited research has been conducted on specific processes (e.g. reparation and mirroring). Conclusion: The present study provides an original research-grounded framework to consider the different nature of mother-infant dyadic processes within a unified dyadic eco-system. Different levels of evidence emerged for the role of diverse mother-infant dyadic processes on infants' and children development. Open questions and future research directions are highlighted.

The COVID-19 pandemic is a global traumatic experience for citizens, especially during sensitive time windows of heightened plasticity such as pregnancy and neonatal life. Pandemic-related stress experienced by mothers during pregnancy may act as an early risk factor for infants’ regulatory capacity development by altering maternal psychosocial well-being (e.g., increased anxiety, reduced social support) and caregiving environment (e.g., greater parenting stress, impaired mother–infant bonding). The aim of the present longitudinal study was to assess the consequences of pandemic-related prenatal stress on infants’ regulatory capacity. A sample of 163 mother–infant dyads was enrolled at eight maternity units in northern Italy. They provided complete data about prenatal stress, perceived social support, postnatal anxiety symptoms, parenting stress, mother–infant bonding, and infants’ regulatory capacity at 3 months of age. Women who experienced emotional stress and received partial social support during pregnancy reported higher anxious symptoms. Moreover, maternal postnatal anxiety was indirectly linked to the infants’ regulatory capacity at 3 months, mediated by parenting stress and mother–infant bonding. Dedicated preventive interventions should be delivered to mothers and should be focused on protecting the mother–infant dyad from the detrimental effects of pandemic-related stress during the COVID-19 healthcare emergency.