Fetal heart rate complexity measures to detect hypoxia

Perinatal hypoxia is a severe condition that may harm fetus organs permanently or even cause dead. When the fetus brain is partially deprived from oxygen, the control of the fetal heart rate (FHR) is affected. We hypothesize that the complex physiological mechanisms of the FHR are perturbed under perinatal hypoxia. To quantify the loss in complexity we measured Sample Entropy (SampEn), Permutation Entropy (PE), and Time Irreversibility (TI). FHR traces were preprocessed to remove artifacts. A database of 32 FHR recordings were acquired with cardiotochography, 15 controls and 16 cases. Resampling methods were used to establish the statistical differences. TI was significantly different for healthy and hypoxia fetuses (-0.38 ± 0.19 vs. -0.21±0.37, p-value=0.063). Entropy indices were higher for healthy fetuses (SampEn:0.33±0.12 vs 0.28 ± 0.09, p-value=0.11; PE:0.72±0.04 vs 0.69±0.07, p-value= 0.12). We also computed temporal and spectral indices but none of them showed significant differences. Complexity measures of the FHR were different for healthy and hypoxia fetuses. These indices may help to early detect hypoxia with less invasive methods.