Assessment of fetal heart rate variability and velocity variability by Doppler velocimetry of the descending aorta at 10-20 weeks of gestation

Objectives Determination of gestational age-related modulations in fetal he art rate and descending aorta blood flow velocity in the early human fetus and comparison of aortic variability data with data obtained from the umbil ical artery. It is hypothesized that these modulations present in the umbil ical artery also occur in the descending aorta. Methods Doppler studies of descending aorta velocity waveforms were perform ed at 10-20 weeks in 55 normal pregnant women. In 24 of the 55 women, Doppl er recordings from both the descending aorta and the umbilical artery were collected. Absolute values and variability of fetal heart rate, peak systol ic and time-averaged velocities were determined from flow velocity waveform s of a least 18 s duration. Results From 10 to 20 weeks of gestation, the descending aorta peak systoli c and time-averaged velocities increased, whereas the fetal heart rate decr eased. The descending aorta peak systolic variability also increased. Howev er, the time-averaged velocity variability and fetal heart rate variability remained constant during the study period. In the subset of 24 women, the fetal heart rate variability and velocity variability data from the descend ing aorta and umbilical artery were not significantly different. Conclusions Reproducible fetal heart rate and velocity variability data can be derived from the descending aorta and umbilical artery. The increase in heart rate variability observed in the umbilical artery was not seen in re cordings obtained from the descending aorta. Different fetal activity state s may be the underlying mechanism for these heart rate variability discrepa ncies.