Flow-velocity profiles of the fetal aorta and umbilical artery in pregnancies complicated by pregnancy-induced hypertension and fetal growth retardation

Sixty-seven women undergoing ultrasonographic evaluation in the high-risk clinic were randomly recruited to be examined by a newly developed computerized method that presents flow-velocity profiles derived from pulsed Doppler-generated flow-velocity waveforms. Each woman had pulsed Doppler flow velocimetry of the fetal aorta and umbilical arteries done. Subjects were either normal controls (N = 20) or had pregnancies complicated by pregnancy-induced hypertension (N = 29), fetal growth retardation (N = 11), or both (N = 7). Distinct patterns of flow-velocity distribution across the fetal aorta and proximal umbilical arteries were identified in the pregnancies characterized by increased placental resistance. At peak systole, normal velocity was maintained only at a narrow area around the center of the vessel, whereas velocity in the rest of the vessel area was markedly reduced. These changes were present in 40 of 47 subjects (85.1%) with complicated pregnancies, whereas 27 of 47 (57.4%) had umbilical artery systolic-diastolic ratios above the 95th percentile. No significant differences between normal and complicated pregnancies were seen during diastole. Our findings suggest that increased placental resistance results in a redistribution of velocities within fetal blood vessels, often before maximal end-diastolic velocity is decreased.