OBJECTIVES: We asked whether maternal or fetal cortisol treatments induced fetal lung maturation and growth restriction compared with betamethasone and whether medroxyprogesterone (MPA) influenced lung maturation.STUDY DESIGN: Pregnant sheep were randomized to receive MPA or saline solution at 100 days of gestation. At 117 days of pregnancy, ewes were randomized to receive maternal or fetal treatments with 0.5 mg/kg betamethasone, four injections of hydrocortisone given over 4.5 hours or saline solution. Body weight and lung maturation were evaluated at 125 days.RESULTS: Maternal betamethasone decreased in birth weight by 16% and induced lung maturation. Fetal cortisol or betamethasone induced only lung maturation. Maternal cortisol caused neither growth restriction nor lung maturation. MPA did not alter lung function in control lambs or in betamethasone-treated preterm lambs.CONCLUSIONS: Maternal cortisol treatments had no apparent effects on the fetus, suggesting that growth restriction caused by betamethasone may result from unidentified effects on the maternal-placental unit.