A PLACEBO-CONTROLLED, BLINDED COMPARISON BETWEEN BETAMETHASONE AND DEXAMETHASONE TO ENHANCE LUNG MATURATION IN THE FETAL MOUSE

OBJECTIVE: To compare the effects of betamethasone and dexamethasone u sed to enhance lung maturity of the fetal mouse. METHODS: Adult CD-1 m ice were administered a single dose of either a placebo or different s trengths of betamethasone (0.01, 0.025, or 0.10 mg) or dexamethasone ( 0.025 or 0.10 mg) on day 14.0 (74%) of gestation. The eight gravid mic e in each treatment cohort were killed on day 16.5 to assess fetal lun g maturity (histologic changes and respiratory patterns) in a blinded manner. Another ten gravid mice in each treatment group were allowed t o deliver spontaneously to assess perinatal outcomes. RESULTS: Compare d with the effects from placebo exposure, the 0.10-mg doses of both be tamethasone and dexamethasone demonstrated enhanced histologic maturat ional changes and improved neonatal respiratory efforts. Betamethasone was twofold to threefold more potent than dexamethasone. The fetal cr own-rump lengths and the fetal body, lung, and heart weights were indi stinguishable among the three treatment groups. Compared with the feta l liver weight in the placebo group (55.0 +/- 2.2 mg), the liver was l ess heavy after exposure to 0.10 mg of betamethasone (45.6 +/- 2.0 mg; P < .005), 0.025 mg of dexamethasone (47.6 +/- 1.7 mg; P < .02), or 0 .10 mg of dexamethasone (43.8 +/- 1.5 mg; P < .001). No significant di fferences were observed between the 0.10-mg treatments of either corti costeroid and placebo for the duration of gestation, litter size, surv ival rate, birth weights, or weight gains to postnatal day 26. CONCLUS ION: A single subcutaneous dose of 0.10 mg of betamethasone was twofol d to threefold more potent than dexamethasone in accelerating fetal lu ng maturity without impairing fetal survival or weight gain. The unexp ected finding of a reduced fetal liver weight with either corticostero id warrants clinical correlation. Copyright (C) 1997 by the Society fo r Gynecologic Investigation.