Differential effects of betamethasone on the fetus between morning and afternoon recordings.

Background: Fetal heart rate (FHR) variation and fetal movements show a diurnal rhythm, a rise in the afternoon and evening compared to morning hours. A previous study showed that reductions in fetal parameters occurring two to three days after betamethasone administration are most likely caused by suppression of the normal rise during the day. Therefore monitoring during the morning could circumvent the suppressive effects of betamethasone.

Objective: To study the effects of betamethasone on fetal diurnal rhythms, by comparing morning and afternoon recordings over five successive days.

Methods: This was a prospective longitudinal study of 20 women at 25-34 weeks of gestation. One-hour recordings of FHR and fetal movements were made on each of five successive days in the morning and afternoon. Betamethasone was administered on day 0 and day 1.

Results: We found no reduction of FHR variation on days 2 and 3 in the morning. In contrast, in the afternoon a reduction of FHR variation occurred on day 2. Time courses of fetal body and breathing movements during the morning were not affected by betamethasone administration.

Conclusions: Transient reductions in fetal movement and FHR variation after glucocorticoid administration are not observed in the morning. For fetal monitoring and especially for assessing trends in fetal heart rate variation and movements with time, morning recordings should be preferably used in the period around glucocorticoid administration.