The effects of maternal betamethasone administration on the fetus.

OBJECTIVE: To examine prospectively the effects of maternal betamethasone administration on fetal heart rate variation, body, breathing and eye movements and the rest-activity cycle.
DESIGN: Thirty-one women on 38 occasions were at risk of premature delivery and received two doses of betamethasone 24 h apart. Gestational age ranged between 26 and 32 weeks. Fetal heart rate was monitored on each of five successive days (0-4) and fetal body, breathing and eye movements were recorded on days 0, 2 and 4.
RESULTS: Compared with the control day before steroid administration (day 0), both long term and short term fetal heart rate variation were reduced on days 2 and 3 (P < 0.01). In one-third of the cases, fetal heart rate variation fell transiently below the lower normal range for gestational age. Body movements were reduced on day 2 by 50% (P < 0.01) due to prolonged periods of inactivity (P < 0.01). Breathing movements were largely absent on day 2 (P < 0.01), but the occurrence of eye movements remained unchanged after betamethasone administration. All values returned to baseline on day 4, indicating that no fetal deterioration had occurred during the course of the study period. Similar responses to betamethasone were observed in five fetuses when studied at re-presentation two weeks later.
CONCLUSIONS: Maternal betamethasone administration causes a considerable but transient reduction in fetal body movements and activity periods, breathing and heart rate variation, without affecting fetal eye movements. Knowledge of this phenomenon is important when assessing the fetal condition. The effect may be due to a glucocorticoid receptor mediated process in the fetal brain.