Objective(s)-Glucocorticoid administration to women in preterm labor improves neonatal mortality and morbidity. Fetal exposure to glucocorticoid levels higher than those appropriate to the current gestational stage has multiple organ systems effects. Some, e.g., fetal hypertension, are maximal at lower than the clinical dose. We hypothesized that the clinical dose has supramaximal lung maturational effects.Study Design-We evaluated the full, half and a quarter the clinical betamethasone dose (12mg/ 70kg or 170μg/kg i.m. twice 24h apart) on fetal sheep lung pressure volume curves (PVC) after 48h exposure at 0.75 gestation. We measured key mRNAs and protein products that affect lung function and total lung dipalmitoyl phosphatidyl choline (DPPC).Results-Full and half doses had similar PVC and total lung DPPC effects. mRNA for SPA, B and D and elastin rose in a dose dependent fashion.Conclusion-Half the clinical betamethasone dose produces maximal PVC improvement in fetal sheep at 0.75 gestation.

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