Power spectrum analysis of heart rate and blood flow velocity variability measured in the umbilical and uterine arteries in early pregnancy: a comparative study

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Abstract
Objective: To compare power spectral derived variability parameters from the fetal side of the placental circulation with those from the maternal side of the placental circulation, during early pregnancy.Methods: Doppler velocity waveforms were obtained from both the umbilical and the uterine arteries in a study group of 40 pregnant women between 10 and 14 (n = 25) and 15 and 20 (n = 15) weeks of gestation. The coefficient of variation of both the beat‐to‐beat heart rate variability and the blood flow velocity variability was determined. The ratio of the integrated low‐frequency components (< 0.2 Hz) and the integrated high‐ frequency components (> 0.2 Hz) from normalized power spectrum analysis (LH‐ratio) was established, to reflect sympathovagal balance.Results: The coefficient of variation and LH‐ratio of fetal heart rate variability constitute only a fraction of the same maternal heart rate variability parameters. Nevertheless a highly significant increase (P < 0.001) in LH‐ratio was demonstrated with advancing gestational age. The coefficient of variation and LH‐ratio of blood flow velocity variability were significantly lower in the fetal umbilical artery only in the 10–14‐weeks' gestation group. Due to a decrease of the maternal uterine blood flow velocity variability parameters with advancing gestational age, statistically equal fetal and maternal values for coefficient of variation and LH‐ratio were found in the 15–20 weeks' gestation group.Conclusions: The increase in LH‐ratio of fetal heart rate variability indicates functional development of the fetal autonomic nervous system at 15–20 weeks' gestation. The umbilical blood flow velocity variability may be secondary to maternal uterine arterial flow variability rather than due to primary changes in fetal cardiovascular function. Copyright © 2001 International Society of Ultrasound in Obstetrics and Gynecology

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