Abstract
Monitoring of fetal heart rate (FHR) is an important measure of fetal wellbeing during the months of pregnancy. Previous works on estimating FHR variability from Doppler ultrasound (DUS) signal mainly through autocorrelation analysis showed low accuracy when compared with heart rate variability (HRV) computed from fetal electrocardiography (fECG). In this work, we proposed a method based on empirical mode decomposition (EMD) and the kurtosis statistics to estimate FHR and its variability from DUS. Comparison between estimated beat-to-beat intervals using the proposed method and the autocorrelation function (AF) with respect to RR intervals computed from fECG as the ground truth was done on DUS signals from 44 pregnant mothers in the early (20 cases) and late (24 cases) gestational weeks. The new EMD-kurtosis method showed significant lower error in estimating the number of beats in the early group (EMD-kurtosis: 2.2% vs. AF: 8.5%, p < 0.01, root mean squared error) and the late group (EMD-kurtosis: 2.9% vs. AF: 6.2%). The EMD-kurtosis method was also found to be better in estimating mean beat-to-beat with an average difference of 1.6 ms from true mean RR compared to 19.3 ms by using the AF method. However, the EMD-kurtosis performed worse than AF in estimating SNDD and RMSSD. The proposed EMD-kurtosis method is more robust than AF in low signal-to-noise ratio cases and can be used in a hybrid system to estimate beat-to-beat intervals from DUS. Further analysis to reduce the estimated beat-to-beat variability from the EMD-kurtosis method is needed.
Highlights
Fetal Heart Rate (FHR) monitoring (1997) by Doppler based cardiotocography (CTG) in the third trimester is a commonly established method to identify fetal compromises
We have applied a method based on computing the kurtosis function on the Intrinsic Mode Functions (IMFs) extracted from the Doppler US technique (DUS) signal to estimate cardiac beat-to-beat intervals
The proper choice of the window size used to compute the kurtosis was important in reducing the error in estimating both the number beats and the beat-to-beat variability
Summary
Fetal Heart Rate (FHR) monitoring (1997) by Doppler based cardiotocography (CTG) in the third trimester is a commonly established method to identify fetal compromises. It has been shown that modern fetal monitors using the Doppler US technique (DUS) do not provide reliable evaluation of FHR variability (Fuchs, 2014). This is due to the changing fetal Doppler signal over time as a result of location changes of fetal heart and the high signal to noise ratio (SNR) which make it very difficult to determine the beat-tobeat intervals (Shakespeare et al, 2001). Abdominal fetal electrocardiography (fECG) has been reported to provides more reliable description of the instantaneous FHR variability than
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