Uteroplacental resistance index: analysis of intra- and interobserver variability

The aim of this study was to assess the intra- and interobserver variability of second-trimester uteroplacental continuous-wave flow velocity waveforms. The left and right uterine and arcuate resistance indices were measured in women having their routine booking scan at 16-24 weeks' gestation. Four experiments assessed the intra-observer between-frame variability, the intraobserver beat-to-beat variability, the intraobserver temporal variability, and the interobserver variability, using the limits-of-agreement method. The intraobserver between-frame variability was greater than the beat-to-beat variability at three of the four sites. The temporal variability was not significantly different between sites. There were wide interobserver limits of agreement with respect to the reference ranges, although they were greater at arcuate sites than uterine sites. These observations suggest that the reproducibility of the resistance index in continuous wave Doppler uteroplacental flow velocity waveforms is poor, particularly from arcuate sites. The uterine site is preferable and descriptive analysis may be better.