Summary. The estimation of fetal umbilical vein and aortic volume blood flow was compared with umbilical artery flow velocity‐time waveform analysis in 42 pregnancies. The volume blood flow measurements were made with a combined linear array B‐mode and pulsed Doppler ultrasound system. The umbilical artery flow velocity‐time waveform analysis was made with either pulsed or continuous wave 2 MHzDoppler ultrasound and the systolic/diastolic (A/B) ratio was used as an index of flow resistance. There was no difference when continuous wave was compared to pulsed Doppler ultrasound as a method of recording flow velocity waveforms. Analysis of the umbilical artery flow velocity‐time waveform was more sensitive (100%‐50%) than the measurement of umbilical vein volume blood flow (ml/kg/min) in the detection of the small‐for‐gestational age (SGA) fetus. The predictive value of a positive test was higher (71%‐45%) while specificity was similar (88%‐81%). Descending aortic volume flow was reduced in only one SGA fetus. The increase in umbilical placental downstream resistance (high systolic/ diastolic ratio) was associated with a reduction in the percentage of fetal aortic blood flow directed to the umbilical placental circulation.
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Giles et al. (1986) studied this question.
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