FETAL AND MATERNAL DIURNAL RHYTHMS DURING THE 3RD-TRIMESTER OF NORMAL-PREGNANCY - OUTCOMES OF COMPUTERIZED ANALYSIS OF CONTINUOUS 24-HOUR FETAL HEART-RATE RECORDINGS

OBJECTIVE: We quantified the presence of diurnal rhythms in various co mputerized fetal heart rate parameters in normal pregnancies to assess their clinical relevance. STUDY DESIGN: Modified cosine analysis was applied to the outcomes of computerized analysis of continuous 24-hour fetal heart rate recordings in 26 normal pregnancies,. Diurnal rhythm s in maternal heart rate and plasma hormones were assessed in 15 and 1 7 pregnancies, respectively. Correlations between maternal and fetal r hythms were calculated. RESULTS: A significant diurnal rhythm in basal heart rate was present in 73% of the fetuses and was closely related to the maternal heart rate rhythm. Diurnal rhythms in heart rate varia bility, accelerations, and activity were present in only 30% to 50% of the fetuses. CONCLUSIONS: The mother entrains fetal diurnal rhythms. The normal variability in neural development may account for the absen ce of diurnal rhythms in some fetuses.