Free urinary cortisol immunoreactive levels in premature and full term infants

Urinary free immunoreactive cortisol excretion was measured in 20 full term, 20 premature and 20 premature newborns of mothers who had been treated with 12 mg betamethasone 48 hours before delivery. In 10 full term newborns delivered normally, values were 40 +/- 20 nmol/mmol creatinine on the first, 23 +/- 8 on the second and 21 +/- 6 on the third day of life. In 10 full term newborns with stressful delivery, the corresponding values were 63 +/- 39, 44 +/- 33 and 32 +/- 17 nmol/mmol creatinine in the first three days of life. The levels of urinary free immunoreactive cortisol of 10 premature newborns delivered without stress were 170 +/- 116, 91 +/- 75 and 70 +/- 61 nmol/mmol creatinine respectively, on days one, two and three of life. Ten premature infants with respiratory distress syndrome had values of 471 +/- 187, 526 +/- 465 and 636 +/- 906 nmol/mmol creatinine, respectively. The 10 premature newborns whose mothers had received betamethasone, had urinary free immunoreactive cortisol levels of 109 +/- 120, 55 +/- 42 and 66 +/- 84 nmol/mmol creatinine, lower than the other premature infants. This difference, however, was not statistically significant. We conclude that premature infants regardless of stress or normal labor have high urinary free immunoreactive cortisol excretion, suggesting that prematurity per se is a potent stress.