References ranges and sources of variation for indices of pulsed Doppler flow velocity waveforms from the uteroplacental and fetal circulation

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Abstract
Summary. Variation in indices used to characterize the maximum frequency outline of waveforms obtained from the uteroplacental and fetal circulations by duplex Doppler ultrasound was studied between observers, over a 24-h period and before and after a meal. No significant differences were found. Reference ranges were derived for three indices, the A/B ratio, the resistance index and the pulsatility index, for waveforms from the fetal descending aorta, umbilical artery, and the placental and maternal sides of the uteroplacental circulation. Indices from waveforms from the uteroplacental circulation demonstrated a fall from 16 to 24 weeks gestation with no change thereafter. The umbilical artery indices demonstrated a continuing fall with increasing gestation but the A/B ratio and resistance index from the fetal descending aorta did not change with gestation. The pulsatility index from the aorta demonstrated a gentle rise.

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