Evaluation of fetal heart rate variability based on automatically determined R-times in a fetal ecg monitor

In 51 healthy fetuses at term, we calculated fetal heart rate variability (HRV) obtained using a fetal ECG monitor which automatically determined RR interval durations. We compared the values of various HRV measures from different domains to those obtained from high quality fetal magnetocardiographic acquisitions in a similar subject group. The comparison showed significant differences in all domains, in particular in HRV measures which quantify short-term variability. Inspection of the ECG RR interval time series suggested inappropriate identification of R-times. Thus, although fetal heart rate and its overall variance may be accurately determined using such monitors, caution should be taken when assessing short-term HRV.