Immediate and delayed effects of antenatal corticosteroids on fetal heart rate: a randomized trial that compares betamethasone acetate and phosphate, betamethasone phosphate, and dexamethasone

Objective: The purpose of this study was to evaluate the role of different formulations and different administration kinetics of antenatal corticosteroid therapy on fetal heart rate. Study design: One hundred five patients who were at high risk for preterm delivery were assigned randomly to receive two injections of betamethasone acetate + phosphate, four injections of betamethasone phosphate, or four injections of dexamethasone phosphate. Computerized fetal heart rate was recorded daily through day 4. Results: The three formulations did not differ in their effect on fetal heart rate, which varied significantly as a function of the time of injection. During treatment (day 0-day 1), fetal heart rate variability increased (+9%, P < .05), as did the number of fetal movements felt by the mother (+60% at day 0, P < .001). After treatment (day 2-day 3), variability fell significantly (−14%, P < .01), as did accelerations (−35% at day 2, P < .01). No modifications were still detectable on day 4. Conclusion: Antenatal corticotherapy is responsible for two different phases of fetal heart rate modifications that do not vary according to the corticosteroid or the dosage regimen. (Am J Obstet Gynecol 2003;188:524-31.)