Time-frequency analysis of fetal heartbeat fluctuation using wavelet transform

Yoshitaka Kimura, Kunihiro Okamura, Takanori Watanabe, Nobuo Yaegashi, Shigeki Uehara, Akira Yajima

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)


We examined whether the nonlinear control mechanism of the fetal autonomic nervous system would change in various fetal states. Eight thousand or more fetal heartbeats were detected from normal, hypoxemic, and acidemic fetuses. Fetal heart Doppler-signal intervals were determined in a high- precision autocorrelation method, and a time series of fetal heart rate fluctuation was obtained. The distribution of the amplitude of temporal fluctuation in the low-frequency component of fetal heart rate frequency was studied using a method of time-frequency analysis called wavelet transform. Spline 4 was used as the mother wavelet function. A gamma distribution was observed from 17 wk of gestation onward. The value of the parameter ν of this gamma distribution was ~1.6 and remained constant regardless of the gestational age or the time of day. The value of ν decreased significantly to 0.77 when the fetus developed acidemia and was 1.51 in hypoxemia and 1.54 in a normal condition. This study elucidates a nonlinear structure of the time series of heart rate fluctuation of the gamma distribution in the human fetus. This technique may provide a new quantitative index of fetal monitoring to diagnose fetal acidemia.

Original languageEnglish
Pages (from-to)H1993-H1999
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Issue number6 44-6
Publication statusPublished - 1998 Dec


  • Fetal acidosis
  • Fetal monitoring
  • Gamma distribution

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)


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