Lung morphometry after repetitive antenatal glucocorticoid treatment in preterm sheep

Antenatal glucocorticoids are thought to be less effective when delivery oc curs more than 7 d after initiation of treatment; therefore, repeat courses are often administered. We examined lung structure after single or repetit ive antenatal glucocorticoid injections in fetal sheep. Pregnant ewes recei ved single or repetitive doses of 0.5 mg/kg betamethasone at 7-d intervals by maternal or fetal injection, beginning at D104 or D114 with delivery at D125, D135, or D146 gestation (term = 150 d). Changes in lung structure wer e more pronounced after repetitive versus single injections. Repetitive fet al or maternal injections beginning at D104 (delivery at D125) resulted in comparable structural changes: alveolar Volume increased by 50 to 80%, alve olar numerical density decreased by 30 to 40%, and pleural and interlobular septal volumes decreased by as much as 70%. Similar changes were seen in a nimals delivered at D135 after repetitive maternal injections beginning at D114. There were no structural differences between control and repetitive b etamethasone animals when delivery was delayed until D146, indicating that betamethasone induced structural changes were reversible.