Regulation of stress physiology across social contexts in prematurely born toddlers

Premature birth increases risk for socio-emotional difficulties and altered autonomic regulation, yet because physiological regulation supports development, dysregulation may have lasting consequences. We evaluated social functioning and physiological regulation in 70 preterm children aged 5.5 years compared to 32 matched full-term controls (Total sample: 59 boys, 43 girls; 98% White). Heart rate and heart rate variability (HRV) were recorded during rest and structured social interactions with the mother and a stranger, including eye contact, conversations, and triadic play. Preterm children demonstrated significantly greater social difficulties and internalizing problems than full-term peers. Across conditions, they exhibited consistently elevated heart rate, whereas HRV patterns were comparable between groups. Specifically, RMSSD-HRV varied by interaction partner (stable with mother, fluctuating with stranger), while HF-HRV reflected general condition effects independent of partner familiarity. Conversation tasks elicited the strongest autonomic activation, with pronounced vagal withdrawal during negative exchanges. In conclusion, preterm children show persistent cardiac hyperarousal and social-behavioral difficulties, yet maintain context-dependent autonomic regulation similar to full-term peers. The distinct sensitivity of HRV indices suggests preserved regulatory mechanisms, indicating that prematurity's physiological signature may reflect heightened baseline arousal rather than impaired regulation.