The dual nature of hypothalamic-pituitary-adrenal axis regulation in dyads of very preterm infants and their mothers

The co-regulation of the hypothalamic-pituitary-adrenal (HPA) axis in mother-infant dyads is thought to be key for infant and child development. Nonetheless, previous literature presents some inconsistencies that might at least partially be due to the presence of risk conditions and the use of different statistical approaches to measure HPA axis co-regulation. Very preterm (VPT) birth represents one of these risk conditions as the early foundation of mother-infant interaction is disrupted. Both VPT infants and their mothers present evidence of altered HPA axis regulation. Nonetheless, the comparison of mother-infant HPA axis co-regulation in VPT infants compared to full-term (FT) ones has not been previously investigated. In this study, 3-month-old (corrected age) VPT infants and FT counterparts with their mothers took part in a well-validated stress-inducing laboratory task (i.e., double Face-to-Face Still-Face, FFSF paradigm). Salivary cortisol samples were obtained before (Baseline) and after (Early reactivity, Late reactivity and Recovery) the FFSF procedure. Dyadic HPA axis co-regulation was assessed at each sample time-point (i.e., in-moment coupling) as well as across samples (i.e., in-time synchrony). Significant in-moment coupling emerged at Baseline, Late reactivity and Recovery for FT infants’ dyads only. An overlying pattern of salivary cortisol trajectories emerged between mothers and infants in the VPT group, whereas a more complex pattern of reciprocal and complementary co-regulation was found for FT infants’ dyads. Although both groups gave evidence of HPA axis co-regulation, dyads of VPT infants appear to be less able to adapt reciprocally and dynamically to stressful conditions. These findings suggest that multiple approaches to account for dyadic HPA axis co-regulation should be used in order to depict the complex pattern of biological rhythms coordination in mother-infant dyads.