A study of fetal sympatho-vagal balance at various gestational periods using the length transform on magnetocardiographic data

In this paper we characterize fetal sympatho-vagal balance by studying the correlation, time shifts, and ratios, between very-low-frequency (VLF), low-frequency (LF), and high-frequency (HF) components in heart rate (HR) variability over time. The HR is obtained from fetal magnetocardiographic (fMCG) recordings at various gestational periods. The frequency components are separated from the HR signal and pre-processed with the Length Transform (LT). The LT represents a temporarily smoothed time course of the data and has the property of highlighting the variability information of the signals over fixed-length windows. Therefore, we compute the correlations, time shifts, and ratios using the transformed data in order to avoid miscalculations and provide accurate quantitative measures. Our results show accordance with previous studies in sympathetic and parasympathetic control systems, and have the potential of characterizing fetal development.