Intra- and interoperator repeatability of the nuchal translucency measurement

Abstract

Objective: The aim of this study was to assess the repeatability of nuchal translucency measurement by well-trained sonographers either experienced or inexperienced with the measurement.

Methods: The nuchal translucency was measured three times by two out of nine operators in 161 pregnant women attending two teaching hospitals. Intra-operator and inter-operator variation was assessed by calculating the standard deviation (SD). Intraclass Correlation Coefficients (ICC) with a 95% lower confidence limit (95% CL) were calculated for each operator and for pairs of operators. Intra- and inter-operator kappa statistics were calculated, after dichotomising the results into a nuchal translucency smaller or larger than 3 mm.

Results: The SD of intra-operator difference was 0.35 mm. The intra-operator repeatability showed ICCs varying from 0.83 to 0.95 for the experienced operators and from 0.47 to 0.83 for the inexperienced. The SD of inter-operator differences was 0.56 mm, 0.46 mm and 0.44 mm, based on one, two and three measurements, respectively. The inter-operator repeatability showed a variation in ICC from 0.74 to 0.95 in pairs of experienced sonographers to 0.51 in one pair inexperienced with the measurement. The kappa value expressing the intra and inter-operator repeatability as being > 3 mm or < 3 mm was 0.88 and 0.85, respectively.

Conclusion: This study supports the finding that the nuchal translucency measurement is reproducible, as long as it is performed by sonographers well trained in the technique of this measurement.