Umbilical artery Doppler blood velocity waveforms in normal and abnormal gestations

Blood velocity patterns in peripheral arteries reflect hemodynamic characteristics, particularly systemic vascular resistance. Doppler blood velocity waveforms in umbilical arteries (UA) indirectly assess placental vascular resistance (P1VR) and therefore an abnormal waveform value may serve as an index of placental insufficiency associated with elevated P1VR. We prospectively studied the ratio of peak-systolic to end-diastolic velocities (A/B ratio) in the UA of 113 normal fetuses on 121 occasions over a period of 4 years. A range-gated, pulsed Doppler, duplex, two-dimensional, real-time echocardiogram (ECHO) allowed placement of the sample volume in the UA by direct vision; hard copy of the tracing was later analyzed. Hand calipers allowed measurement of the fetal cardiac cycle length (RR) and A/B ratio, which were compared with gestational age (EGA), echo-derived total cardiac dimension (TCD), and aortic root size (AO). Normative data were analyzed by least squares linear regression and compared to data in several high-risk groups. In the normal fetus, there was an orderly pattern with advancing gestational age of linearly decreasing A/B ratio and increasing TCD, AO, and RR. The A/B ratio varied inversely with TCD and AO, but was independent of RR. In a group of 20 hypertensive patients, 6 had elevated A/B ratios; of 18 diabetic pregnancies, 4 had elevated A/B ratios. In other high-risk groups, 4 of 21 patients were abnormal: sickle-cell disease (1 case), systemic lupus erythematosus (1 case), and intrauterine growth retardation (2 cases). In conclusion, Doppler A/B ratios in the UA of normal patients, like cardiac size, show an orderly pattern of change with EGA independent of RR.(ABSTRACT TRUNCATED AT 250 WORDS)