A randomised controlled comparison of betamethasone with dexamethasone: effects on the antenatal fetal heart rate

Objective To compare the effects of maternal administration of betamethasone and dexamethasone on fetal heart rate, using computerised numerical analyses, and to examine the association between changes in short term variation and the timing and indication for delivery. Setting John Radcliffe Hospital, Oxford. Sample Fifty-nine women with singleton pregnancies, who were at risk of delivery before 34 weeks of gestation, had received no steroids in the preceding week and could give informed consent. Methods Women were randomised on a double-blind basis to receive either betamethasone or dexamethasone. The fetal heart rate was recorded (60-minute duration at similar times of day) before steroid administration and on each of the following two days; changes were measured by computerised analyses. Main outcome measures Changes in short term variation and long term variation of fetal heart rate or the number of fetal movements. Statistical analysis was nonparametric. Results Betamethasone and dexamethasone had no differential effects on the computerised cardiotocography. However, both steroids decreased baseline fetal heart rate, increased long term variation, increased short term variation, and decreased fetal movements on the first day after steroid administration, and decreased high fetal heart rate variation and decelerations on the second day. Among 13 women who were delivered within one week of steroid administration, smaller rises in short term variation on day one were associated with delivery for fetal indications. Conclusions Both betamethasone and dexamethasone produced transient, unexplained changes in the fetal heart rate over the two days following steroid administration. Larger changes in short term variation were associated with fetal wellbeing. It is important to recognise that such changes are a physiological response of the human fetus to steroid administration.