Fetal and maternal diurnal rhythms during the third trimester of normal pregnancy: Outcomes of computerized analysis of continuous twenty-four—hour fetal heart rate recordings

Objective: We quantified the presence of diurnal rhythms in various computerized 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 rhythms in maternal heart rate and plasma hormones were assessed in 15 and 17 pregnancies, respectively. Correlations between maternal and fetal rhythms 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 variability, 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 absence of diurnal rhythms in some fetuses.