PITUITARY-ADRENAL RESPONSE IN PRETERM VERY-LOW-BIRTH-WEIGHT INFANTS AFTER TREATMENT WITH ANTENATAL CORTICOSTEROIDS

Antenatal corticosteroids have been widely used for the prevention of respiratory distress syndrome in preterm neonates, yet little is known about their effects on the hypothalamic-pituitary-adrenal axis in the se infants. We prospectively evaluated pituitary-adrenal function in 6 1 preterm (<32 gestational weeks), very low birth weight (<1500 g) inf ants on days 7 and 14 of life using the human CRH stimulation test. Th e baseline and poststimulation plasma ACTH and serum cortisol concentr ations did not differ significantly between infants whose mothers rece ived no antenatal corticosteroids, and those whose mothers received 1- 2 doses or >2 doses (mean 7.2 doses) of prenatal dexamethasone (P = > 0.12). The number of doses of dexamethasone and the time intervals bet ween the last dose of drug and delivery did not significantly affect t he pituitary-adrenal responsiveness on days 7 and 14 of life. Among in fants who did not require mechanical ventilation at the time of the hu man CRH test, significantly higher plasma ACTH (P < 0.014) and lower s erum cortisol concentrations (P < 0.02) were found on day 14 than on d ay 7. In contrast, none of the poststimulation hormone concentrations were significantly different in ventilated infants between days 7 and 14. The relationship between the blood hormone concentrations in each time epoch (day 7 and day 14) and possible confounding factors includi ng gestational and postconceptional age, birth weight, sex, Apgar scor es, mode of delivery, single or higher order births, and mode of venti lation were determined. Plasma ACTH concentrations on day 7 were found to be significantly higher in ventilated than in nonventilated infant s (P = 0.006). However, none of the aforementioned factors correlated significantly with plasma ACTH concentrations on day 13. Serum cortiso l concentrations on day 7 were significantly higher in infants of grea ter gestational age (P = 0.039) and birth weight (P = 0.013), with low er Apgar scores at 1 and 5 min (P = 0.021 and P = 0.049, respectively) , and in those delivered vaginally (P = 0.047). Similarly, serum corti sol concentrations on day 14 were found to be significantly higher in infants with lower Apgar scores at 1 and 5 min (P = 0.011 and P = 0.01 4, respectively) and in infants requiring mechanical ventilation (P = 0.013). Our results suggest that single or multiple courses of antenat al dexamethasone have no long-lasting suppressive effects on pituitary -adrenal function in preterm, very low birth weight infants. Maturatio n of pituitary function appears to be more advanced than adrenal funct ion. The organ's ability to respond appropriately to various stressful stimuli indicates that the pituitary-adrenal axis is highly responsiv e at these early gestational ages.