Non-linear Methods Predominant in Fetal Heart Rate Analysis: A Systematic Review

Figures

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  Figure 1. PRISMA flow diagram and non-linear methods most applied in fHR. DFA, detrended fluctuation analysis; FD, fractal dimension; HE, Hurst exponent.

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  Figure 2. The number of papers, covered by the systematic review, that applied each method. The blue circle represents entropy, the green square represents compression, the black triangle represents fractal analysis, and the red star represents wavelet.

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  Figure 3. Entropies by year. The colors and symbols represent the different measures of entropy. The blue circle, green square, black triangle, and star red represented Shannon entropy, approximate entropy, sample entropy, and multiscale entropy, respectively.

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  Figure 4. Papers using compression in fetal heart rate, by year. The red circle represents the Lempel-Ziv compressor and the blue square represents the other compressors.

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  Figure 5. Papers using fractal analysis in fetal heart rate, by year. The blue circle represents the fractal dimension measure, the green square represents the detrended fluctuation analysis, the black triangle represents the Hurst exponent, the red star represents the multifractal analysis.

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  Figure 6. The wavelet families most used in fHR analysis, by year. The colors and symbols represent the wavelet families. The black circle, blue triangle, purple diamond plus, green square, and star red represented Daubechies family, spline family, symlet family, coiflet family, and other families, respectively.

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  Figure 7. The five most cited research objectives of the papers that applied non-linear methods in fHR, by year of publishing. The colors and symbols represent the different research objectives. The blue circle, cyan square, star red, green triangle, and black diamond plus represent maturation, hypoxia, intrauterine growth restriction, fetal distress, and signal processing, respectively.