Plasma cortisol concentration in newborn infants.

Plasma cortisol was measured in cord and neonatal blood. Cortisol concentration in neonates decreased rapidly during the first three days after delivery and thereafter remained at an almost constant level. The more the delivery was stressful, the higher the cortisol in the 1-day-old infant, but the concentration came down to the same level as in the less stressful delivery on the 3rd day of the infants' life. The cortisol level in vaginal delivery after spontaneous labor was not different from that in vaginal delivery after oxytocin induced labor. Cortisol in small-for-date infants or infants with hyperbilirubinemia was lower than in average-for-date infants or infants without hyperbilirubinemia.