Blood velocity waveforms of the fetal aorta in normal and hypertensive pregnancies.

Blood velocity waveforms were studied using a combination of real-time and Doppler ultrasonic equipment, a spectral analyzer, and on-line computer in the thoracic descending aorta of the human fetus. In 43 normal pregnancies (weeks 30 to 42) the median of mean velocity was 26.5 (24.1 to 27.9) cm/sec, that of the end-diastolic velocity 10.9 (7.9 to 13.4) cm/sec, the velocity acceleration 718.9 (620.3 to 844.1) cm/sec2, the resistance index 0.84 (0.80 to 0.89), and the pulsatility index was 2.49 (1.94 to 3.10). No differences in these values were observed in the fetuses of noncomplicated hypertensive pregnancies (N = 32), whereas the resistance index increased and the mean velocity and end-diastolic velocity decreased if fetal growth retardation was associated with maternal hypertension (N = 14). In the subgroup of fetal distress (N = 6), all of these parameters except velocity acceleration differed from the normal values, reflecting increased peripheral vascular resistance. This method may be of value in the follow-up of fetal well-being in risk pregnancies by giving an early sign of hemodynamic changes in developing hypoxia.