Abstract: Signal change of fetal heart rate is reflected by the function of the circulatory system and the central nervous system. Understanding the dynamics behavior of fetal heart rate is a kind of simple method to infer the situation of fetus in the uterus. According to the characteristic of FHR signal belonging to the short data time series, the FHR signal was analyzed by means of the surrogate data method combined with correlation dimension, the largest Lyapunov exponent and complexity which can identify chaotic features. The research indicates that there are remarkable discriminations between the FHR signal and the surrogate data produced by two groups of two kinds of null hypotheses respectively, indicating that the FHR signal has the nonlinear components and chaos characteristic quantity criterion S＞2, which explains that the FHR signal has nonlinear chaos characteristic.

Key words: fetal heart rate, surrogate data, nonlinear features, chaos