Blood flow velocity waveforms in the descending fetal aorta: comparison between normal and growth-retarded pregnancies.

A linear array real-time transducer was combined with a pulsed Doppler transducer to study and compare the mean blood flow velocity waveform in 77 normal pregnancies and 12 cases of intrauterine growth retardation. All pregnancies were in the third trimester. In normal pregnancies the peak velocity, end diastolic velocity, and pulsatile index remained unchanged with increasing gestational age. End diastolic velocity was lowered or at zero level (high pass filter level), and the pulsatile index was elevated in most cases of severe intrauterine growth retardation. Peak velocity related closely with the quality of the heart rate patterns and the condition of the infant at birth.