Symbolic dynamic and frequency analysis in foetal monitoring

Foetal heart rate variability is widely considered an important parameter to assess foetal reactivity and wellbeing. Traditional approaches to analyze foetal heart rate and its variability, such as Time and Frequency Domain Analyses, have shown some limitations, due to their inability to highlight nonlinear dynamics potentially relevant. Hence, in the last decades, nonlinear analysis methods have gained a growing interest and the integration of parameters derived from these techniques and traditional ones could be a way to improve the assessment of foetal development and/or distress. In this work, we proposed a comparison between new index obtained with a nonlinear analysis (Symbolic Dynamic Analysis) and more traditional parameters computed by the power spectral density of the foetal heart variability signals (Frequency Domain Analysis). A dataset of 579 cardiotocographic signals from healthy foetuses, recorded from the 24th to the 42th gestation week, was examined using both above-mentioned methods. The obtained results demonstrate that Symbolic Dynamics, as much as Frequency Domain Analysis, could be a useful tool in foetal development assessing.