Mode of delivery modulates physiological and behavioral responses to neonatal pain.

Objective: To study whether the mode of delivery alters pain expression.

Study Design: Full-term infants born by vaginal delivery or elective caesarean section were observed following high- and low-intensity pain stimuli, with recording of electrocardiogram, facial expression and vocalization.

Result: Graded physiological and behavioral responses occurred, with greater responses to higher than lower intensity pain stimuli. Elevation in heart rate following both stimuli increased with time after vaginal delivery. Infants delivered by elective caesarean section showed stronger facial expressions and briefer time in vocalizations response to both interventions.

Conclusion: Diminished responses following vaginal delivery suggest that physiological events associated with a normal delivery reduce the physiologic and sympathoadrenal activation by nociceptive mechanisms. Pain and stress reactivity appear to be inhibited during fetal life and sensory inputs during vaginal delivery may reverse this inhibition. To minimize neonatal pain, we recommend that postnatal invasive procedures to be performed shortly after vaginal birth.