Interobserver variability in the measurement of fetal middle cerebral artery peak systolic velocity in a tertiary fetal medicine unit

Abstract

Objectives: To investigate the interobserver variability of fetal middle cerebral artery (MCA) peak systolic velocity (PSV) Doppler measurements in a tertiary fetal medicine unit. Methods: This was a prospective cohort study of pregnant women between 22 and 34 weeks of gestation who underwent fetal MCA-PSV Doppler velocimetry by a paired combination of operators. A set protocol was followed; ease of scanning was recorded and three quality assurance parameters were analyzed. The interobserver variability was determined. In addition, individual operator characteristics were determined by analyzing the variation of each operator relative to all his/her paired colleagues, and their quality assurance parameters. Results: Two hundred and eighty-five women had completed paired fetal MCA-PSV Doppler measurements. Eighty-three (29%) of the ultrasound examinations requested were for suspected fetal anemia and 202 (71%) were for other obstetric indications. The interobserver variation was less than 10% in 78% of the paired MCA-PSV Doppler measurements whereas 99% had less than 15% variation. The intraclass correlation coefficient of each operator when compared with all his/her colleagues ranged from 0.82 to 0.95. The overall mean variability of the MCA-PSV recorded by a given operator, relative to all his/her paired colleagues, ranged from +5.26% to -6.47% in all but one operator whose value was +13.5% (standard deviation factor, 1.13-1.22). Logistic regression analysis, using a 10% or greater variation in MCA-PSV as a binary outcome variable, showed a significant difference when inappropriate angle correction was detected (P < 0.001). Conclusions: Clinically acceptable interobserver variability was obtained in fetal MCA-PSV Doppler measurements. Inappropriate angle correction was found to be a significant predictive factor for increased interobserver variability. Analysis of mean variation identified operators who were outliers enabling quality assurance within the unit. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.