Behavioral and cortisol responses to stress in newborn infants: Effects of mode of delivery.

Suboptimal birth characteristics have been associated with altered reactivity to stress in infants. However, previous studies have not controlled for mode of delivery, which may influence the neonatal onset of stress responses. The present study assessed stress-related behavior and salivary cortisol before and after an inoculation at two hours after birth, and compared infants born through VD (N=70) and elective CS (N=72). The results indicated that overall stress behavior and body movements were increased immediately after inoculation in infants born through CS compared to VD. Infants born through CS did not show significant cortisol increases following inoculation and their overall cortisol reactivity (i.e., AUCG) was lower compared to infants born through VD. However, unexpectedly, cortisol levels in infants born through VD were highest before inoculation and subsequently decreased. Cortisol was significantly related to behavior in both groups, but in opposite directions. These results support the view that mode of delivery influences neonatal stress reactivity, although future studies should try to disentangle the effects of mode of delivery and related variables.