OBJECTIVE: We determined the effect of a single direct fetal injection of corticosteroid and thyroid hormones on postnatal pulmonary function in preterm lambs.

STUDY DESIGN: Initially fetal sheep (126 days' gestation) randomly received saline solution, betamethasone (Celestone Soluspan, 0.5 mg/kg), betamethasone plus triiodothyronine (5 μg/kg), or betamethason plus thyroxine (15 μg/kg) as a single injection. Forty-eight hours later (128 days' gestation) the tetuses were delivered and ventilated for 50 minutes. In a second protocol fetuses were delivered at 128 days' gestation, after only 24 hours of hormone exposure.

RESULTS: Betamethasone treatment improved compliance nearly twofold after 24 or 48 hours of exposure. Efficiency of ventilation also improved after steroid therapy; this effect was augmented 48 hours after thyroxine exposure (but not triiodothyronine). No thyroxine effect was noted after 24 hours of exposure. Maximal lung volume increased by 80% after steroid treatment and doubled in response to combination betamethasone and thyroxine therapy. Alveolar pool sizes of saturated phosphatidylcholine and surfactant protein A were comparable for all groups exposed for 48 hours.

CONCLUSION: A single fetal exposure to betamethasone improves postnatal pulmonary function after 24 or 48 hours. Addition of thyroxine (but not triiodothyronine) augments this effect at 48 hours.