stress response. stress was measured with salivary cortisol, which is highly correlated with plasma cortisol in preterm infants. normal values for preterm infants have not been well established;however, in a study of 48 newborn with a mean gestitional age of 30 weeks and birth weights of 1085 grams salivary cortisol levels ranged from below detectoion to 3.6 mg/dl