The choice of index for umbilical artery Doppler waveforms.

Umbilical artery Doppler waveforms acquired from 211 patients were used to investigate the power of different waveform indices in predicting antenatal fetal compromise. Waveform indices were calculated using a BBC microcomputer. The specificity at 100% sensitivity for detection of antenatal fetal compromise was not significantly different for resistance index, pulsatility index, normalised resistance index and normalised pulsatility index, and was approximately 80%. For the indices of resistance time and downslope the specificity was significantly lower. This similarity in the power of a number of indices in the detection of antenatal fetal compromise suggests that standardisation to one of the simpler indices such as resistance index or pulsatility index could be adopted.