Self-similarity behavior characterization of Fetal Heart Rate signal in healthy and Intrauterine Grow Retardated fetuses

In this paper we deal with the problem of the interpretation of the fetal heart rate (FHR) signal. From literature is known that FHR contains both linear and non linear components. Starting from this consideration we analyzed FHR as a fractal time series and we evaluated its self similarity behavior using the Hurst\´s coefficient (H). We first evaluated the stationarity of FHR time series and then we estimated H with Detrend fluctuation analysis (DFA) method. We calculated Hurst\´s coefficient for healthy fetuses and for fetuses affected by intrauterine grow retardation (IUGR). Results provided H=0.350plusmn0.064 (avgplusmnstd) for healthy patients and H=0.461plusmn0.059 for IUGR. It is also shown that IUGR patients exhibit a "less non-stationary" and longer-memory behavior than normals with a reduced information content of FHR signal. We propose for this phenomenon a physiological explanation connected with the abnormal autonomic nervous system development of IUGR patients