Objective: To determine the effects of a single course of maternally administered dexamethasone on preterm fetal sheep in utero.
Design: Prospective randomised controlled trial.
Setting: University laboratory.
Sample: Pregnant sheep at 0.7 of gestation.
Methods: Pregnant ewes at 103 days of pregnancy (term = 147 days) were given two intramuscular injections of vehicle (n= 7) or 12 mg of dexamethasone (DEX; n= 8) 24 hours apart. Fetuses were continuously monitored for five days.
Main outcome measures: Fetal mean arterial blood pressure, carotid and femoral arterial blood flow and vascular resistance, heart rate, heart rate variability, fetal plasma cortisol and ACTH and fetal body movements.
Results: DEX injections led to an acute increase in mean arterial blood pressure with a rise in carotid and femoral vascular resistance, a fall in femoral arterial blood flow, and a brief fall in fetal heart rate followed by significant tachycardia. From 24 hours after the injections, mean arterial blood pressure and vascular resistance returned to control values, however, a mild tachycardia [200 (3) vs 184 (4) bpm, P < 0.05] and loss of the circadian pattern of fetal heart rate variability persisted until the end of recording. Plasma ACTH and cortisol were markedly suppressed by DEX (P < 0.05), with values returning to control levels 32 and 72 hours after the first injection, respectively. There was no effect on basal fetal heart rate variability, body movements, carotid arterial blood flow, or the circadian pattern of fetal heart rate.
Conclusion: In contrast to previous experiments utilising direct fetal infusion of steroids, maternal administration of DEX was associated with only transient hypertension.