Clinical trial of umbilical artery Doppler waveform quality indices.

The ability of two Doppler waveform quality indices to discriminate between high- and low-quality waveforms was tested using 427 sets of umbilical artery Doppler waveforms from patients. The waveforms had been acquired using a 4-MHz continuous-wave Doppler unit. The quality indices (QI) were based on an assessment of the degree of noise of the maximum frequency envelope of the waveforms, and were first a correlation between successive waveform envelopes (QI1), and, second, a sum of local linearity measures (QI2). The sets of waveforms were graded subjectively according to the clarity of the outline of the waveforms, the degree of interference in the region of the spectrum above the outline, and in terms of the degree of variability caused by fetal breathing. At 90% sensitivity for detection of low-quality waveforms according to a high envelope clarity score, the specificities were 68.2% and 52.7%, respectively, for QI1 and QI2. QI1 was independent from pulsatility index and waveform length, but showed strong dependence on fetal breathing. QI2 showed strong independence from pulsatility and fetal breathing and reasonable independence from waveform length. Both QI1 and QI2 performed poorly when there was a large degree of noise in the region of the spectrum above the envelope; however, this poor performance was often related to the inability of the maximum frequency follower to estimate correctly the maximum frequency envelope in those conditions so that the high waveform quality values reflected the erroneous calculation of pulsatility index in those cases.