Minimum interval from fetal betamethasone treatment to postnatal lung responses in preterm lambs

OBJECTIVE: We hypothesized that fetal betamethasone exposure for <24 hours would improve postnatal lung function in preterm lambs. STUDY DESIGN: Singleton fetal sheep were randomized to receive by ultrasonographically guided fetal injections of 0.5 mg/kg betamethasone or saline solution either 8 or 15 hours before preterm delivery and postnatal assessment of lung function. RESULTS: After the 15-hour fetal treatment-to-delivery interval, betamethasone-treated lambs had twofold improvement in compliance and lung volumes, a fourfold to fivefold decrease in edema index, and higher blood pressures than saline solution–treated lambs. Postnatal lung function or lung volumes did not improve for the 8-hour treatment-to-delivery interval, although betamethasone decreased the pulmonary edema and increased the postnatal blood pressure. CONCLUSIONS: The minimal interval from fetal exposure to corticosteroids to delivery for improved postnatal lung function was between 8 and 15 hours. Corticosteroid effects on pulmonary edema and blood pressure occurred within 8 hours. (AM J OBSTET GYNECOL 1996;174:1408-13.)