Assessment of fetal development by HRV and chaotic global techniques

Introduction: Fetal heart rate and its variability during the course of gestation have been extensively researched. The overall reduction in heart rate and increase in fetal HRV is associated with fetal growth and the increase in neural integration. The increased complexity of the demands on the cardiovascular system leads to more variation in the temporal course of the heart rate which has been shown to be refl ected in measures of complexity. The aim of this work was to investigate novel complexity measures with respect to their ability to quantify changes over gestational age in individual fetuses consistently and in a stable manner. Methods: We examined 215 fetal magnetocardiograms (FMCG), each of 5 min duration, in 11 fetuses during the second and third trimesters (at least 10 data sets per fetus). From the FMCG we determined the fetal RR beat durations. For each 5 min time-series of RR intervals we then calculated Shannon entropy, high spectral entropy, high spectral Detrended Fluctuation Analysis, spectral Multi-Taper Method as well as the standard deviation and two commonly used complexity measures: Approximate Entropy and Sample Entropy. For each subject and HRV measure, we performed regression analysis with respect to ges tational age. The coeffi cient of determination R 2 was used to es timate ‘goodness-of-fi t’, the slope of the regression indicated the strength of the individual dependency on gestational age. Results: We found that the new complexity measures do not outperform ApEn. Conclusion: This study has now rejected the hypothesis that the spectral complexity measures outperform those applied previously.