Transient loss of the diurnal rhythms of fetal movements, heart rate, and its variation after maternal betamethasone administration.

Antenatal betamethasone administration to enhance fetal lung maturation is associated with transient reductions in fetal heart rate (FHR) variation, breathing, and body movements 2 d after the first dose (d 2). This study examines whether steroid administration affects the natural diurnal rhythms of fetal variables. Sixteen women at 27-32 wk of gestation received two doses of betamethasone 24 h apart. One-hour recordings of FHR, breathing, and body movements were made in the morning, afternoon, and evening of d 2, and again in the morning of d 3. Repeat recordings were obtained at 4-6 d later from 9/16 women. Maternal blood samples were obtained with each recording to determine ACTH and cortisol. No diurnal rhythm was present for FHR, FHR variation, breathing, and body movements on d 2. This resulted from suppression of the expected natural rise in body and breathing movements, and heart rate variation in the course of the day. Suppression of the diurnal rhythm of body movements depended on gestation (R = -0.89; p < 0.01). All variables showed diurnal rhythms 4-6 d later. Maternal ACTH and cortisol diurnal rhythms were completely suppressed on d 2. Four to six days later, the normal diurnal pattern was resumed, although absolute levels of ACTH and cortisol were still suppressed. We conclude that maternal betamethasone administration transiently abolishes the fetal diurnal rhythms of heart rate and its variation, breathing, and body movements.