Adrenal function in preterm infants
The fetal zone of adrenal cortex persists after birth in preterm infants, whereas in full term it involutes. The reason for this difference is not known. This study set out to examine this problem by observing changes in adrenal function in infants born prematurely. Twenty-two infants of mean gestation 27.9 weeks and mean birth weight 946 g were studied longitudinally between 170-360 days postconceptional age, by sequential measurements of plasma cortisol, cortisone, DHEAS, urinary steroid metabolites, and adrenal ultrasound scans. The study confirmed persistence of the fetal zone of the adrenal gland in preterm infants as judged by continued excretion of 3β-OH-5-ene steroids in the urine and elevated levels of DHEAS in the plasma. In preterm infants urinary 3β-OH-5ene steroids and plasma DHEAS declined after term (expected date of delivery) suggesting a gestation-related change in fetal zone activity rather than a birth-related change. The low fetal ratio of circulating F:E persisted in preterm infants even beyond term, but plasma cortisol, although lower than in adults, was 10 times higher than in the fetus, and extremely high in very stressed infants. The fetal zone of the adrenal gland in preterm infants did not appear to be controlled by ACTH alone, as fetal zone steroids were excreted in the urine in the absence of ACTH. In two cases, the persistence of the 3β-OH-5-ene steroids in preterm infants was associated with virilisation in female infants. Ultrasound scanning was not found to be a reliable means of measuring the adrenal gland in preterm infants, and size on ultrasound did not relate to adrenal fetal zone activity. Changes in steroid metabolism were demonstrated by examining changes in urinary steroid metabolites.