Assessment of wireless transabdominal fetal heart rate monitoring through linear and entropy indices

Abstract

Introduction: Fetal heart rate (FHR) monitoring is essential to assess fetal well-being during labor. Traditional methods using Doppler ultrasound (US) and fetal scalp electrodes (FSE) have limitations, including restricted maternal movement. A potentially beneficial non-invasive alternative is wireless transabdominal fetal electrocardiography (TAfECG). This study aimed to compare the quality and reliability of TAfECG to US and FSE for FHR monitoring during the first stage of labor using linear and entropy indices. Material and Methods: This secondary analysis used data from a primary cross-sectional study. FHR recordings were obtained simultaneously from US, FSE, and TAfECG. Linear time-domain indices, including mean FHR (mFHR), standard deviation of FHR (sdFHR), long-term irregularity index (LTI), delta FHR (deltaFHR), short-term variation (STV) and interval index (II), were calculated. Linear frequency-domain indices comprised total power (TP), very low frequency (VLF), low frequency (LF), movement frequency (MF), high frequency (HF), and the ratio LF/(MF+HF). Approximate entropy (ApEn) and sample entropy (SampEn) were also determined. The three modalities were compared using non-parametric confidence intervals, Friedman test, Dunn-Bonferroni post-hoc test, and Kendall's Rank Correlation Coefficient. Disagreement analysis employed the measure dAB. Results: 10 FHR recordings were available for analysis. Regarding linear indices, only mFHR, deltaFHR, and HF showed significant differences between modalities. All entropy indices displayed significant differences, primarily between TAfECG and FSE. Strong correlations between the modalities were observed for half of the indices, with exceptions including deltaFHR, STV, II, MF, HF, LF/(MF+HF), and some ApEn/SampEn values, particularly between TAfECG and the other modalities. Disagreement was highest for MF, HF, and LF/(MF+HF) and moderate for entropy indices, often higher between TAfECG and FSE. Conclusions: This study suggests that TAfECG provides FHR data comparable to US and FSE in terms of most linear indices, potentially indicating adequate FHR capture. However, significant differences in entropy indices as well as lower correlations and higher disagreement for specific frequency bands and a few entropy indices warrant further investigation. Larger studies to confirm or refute these findings and elucidate its clinical implications for identifying fetuses at risk could substantiate the adequacy of TAfECG as a non-invasive alternative for FHR monitoring during labor.