Comparison between a newly developed PC-based Doppler umbilical artery waveform analyser and a commercial unit
Objectives. To determine the accuracy of the resistance index (RI) of flow velocity waveforms of the umbilical artery measured using a newly developed PC-based continuous wave Doppler device (Umbiflow) with regard to systematic and random variations when compared with a commercial standard (Vasoflow). Design. A cohort study. Setting. The fetal evaluation clinic (FEC) at Tygerberg Hospital. Subjects. Patients referred to the FEC at Tygerberg Hospital with suspected chronic placental insufficiency. Outcome measures. The correlation coefficients indicating the strength of the relationship between the two devices and their agreement using the method of Bland and Altman. Results. A total of 248 patients were studied. The mean RIs of the first Doppler assessment were 0.69 (standard deviation (SD) 0.11) and 0.67 (SD 0.11) using the Vasoflow and Umbiflow respectively. The Pearson's correlation coefficient comparing the RI of the first test was 0.85. The degree of agreement between the two methods was excellent, the mean differences being very small (< 0.024) with tight confidence intervals. One hundred and ninety-four patients (78.2%) of patients remained in the same percentile category with both the Vasoflow and Umbiflow. Conclusions. The accuracy of the Umbiflow has been proved. A non-significant trend towards slightly lower values needs to be considered. This could be addressed by changing the percentile cut-off to slightly lower values.