Transient reduction in fetal activity and heart rate variation after maternal betamethasone administration.

We studied the short-term effects of maternal betamethasone administration on fetal well-being by recording of fetal movement and heart rate patterns. In 13 women at high risk of preterm delivery (26-32 weeks), eighty 1-h recordings were made of fetal body and breathing movements and fetal heart rate (FHR) and its variation during 5 consecutive days. Betamethasone was administered in two doses 24 h apart after a control recording had been made. After two doses of betamethasone, fetal body and breathing movements and FHR variation were considerably reduced (P < 0.01), but returned to normal after treatment was discontinued. FHR variation was transiently below the lower normal range in 46% of the cases. We conclude that maternal betamethasone administration results in a considerable reduction in fetal movements and FHR variation which may erroneously be interpreted as deterioration of the fetal condition. Knowledge of these transient changes is of significant clinical importance as it may prevent iatrogenic delivery because of suspected fetal distress. The observed effects are possibly mediated by centrally located glucocorticoid receptors.