Diurnal and other variations in fetal movement and heart rate patterns at 20–22 weeks

Abstract

It was investigated when diurnal and other variations in fetal movements and in heart rate pattern emerge during the course of pregnancy. Real-time ultrasound observations were made at 13 weeks of gestation in 7 nulliparous women and at 20–22 weeks in 10 nulliparous women. The observations took place at 0800, 1300 and 2200 and lasted 60 min/session at 13 weeks and 120 min at 20–22 weeks. The fetal heart rate was recorded for 24 h at 20–22 weeks using electrocardiographic electrodes. No diurnal variations were found for any of the movement patterns at 13 weeks. At 20–22 weeks, however, significant diurnal changes were observed in the total activity, the incidence of general movements and the breathing movements, with the lowest values in the morning and the highest during the evening. Fetal breathing movements already appeared to be related to maternal meals at 20–22 weeks as their incidence was significantly lower during the third hour after meals compared to the second hour. The rank order of the incidence of movements (from high to low incidence) was fairly constant over the course of the day both at 13 and at 20–22 weeks. This confirms earlier findings that the rank order of movements is strictly age dependent. Diurnal rhythms were observed for both the fetal heart rate and its variation. The fetal heart rate was lowest between 2400 and 0600 and the heart rate variation was lowest between 0600 and 1100. The incidence of accelerations and decelerations showed no systematic fluctuations over the 24-h period. Decelerations occurred more frequently than accelerations. Episodes of high heart rate variation were associated with an increased incidence of general movements. The various diurnal variations over 24 h at 20–22 weeks generally followed the same temporal sequence as those found near term, although the changes were considerably smaller.