Chaotic and periodic heart rate dynamics in uncomplicated intrauterine growth restricted fetuses

We studied how chaotic and periodic heart rate dynamics differ between norm al fetuses (n = 192) and uncomplicated intrauterine growth restricted fetus es (n = 86), aged 31-42 weeks of gestation. We analyzed each fetal heart ra te time series for 25 min. We quantified the chaotic dynamics of each fetal heart rate time series by correlation dimension. The periodic dynamics wer e analyzed by power spectral analysis. The correlation dimension and, there fore, the complexity, of the heart rate dynamics of the uncomplicated intra uterine growth restricted fetuses was significantly lower than that of the normal fetuses, which was marked at 38-42 weeks of gestation. The low-frequ ency (0.04-0.15 Hz) component and, therefore, the periodicity of the low-fr equency range was significantly higher than that of the normal fetuses duri ng all the gestational weeks. These results mean that, although the intraut erine growth restricted fetuses are not severely compromised, the overall i ntegrity of their cardiovascular control is impaired, especially at term; a nd sympathetic modulation is increased, both of which may contribute to inc reased perinatal mortality. (C) 1998 Elsevier Science Ireland Ltd. All righ ts reserved.