Nuchal translucency measurement: are qualitative and quantitative quality control processes related?

Two types of quality assurance processes for nuchal translucency (NT) measurement have been described: qualitative through review of images and quantitative comparison of operator's specific NT distribution to reference distributions. The aim of this study was to assess the results of these two approaches.

Prospective evaluation of sonologists affiliated to the French Ultrasound College who first underwent qualitative evaluation based on the College Français d'Echographie Foetale (CFEF) score. During one year, those same sonologists measured the NT for Down syndrome screening purposes. The operator's specific NT distributions were compared to their CFEF score, their number of unsatisfactory images and their number of NT measurements per year.

The study involved 1726 sonologists who performed 174 722 first-trimester examinations. Mean (SD) quantitative score was 23.4/32 (+/-7.4). The median [inter-quantile range] number of examinations per sonologist was 69 [37; 123]. The median [range] NT multiples of the mean (MoM) value was 0.81 [0.46; 1.22]. NT (MoM) absolute deviation from 1 MoM was significantly correlated with mean score obtained (R(2)  = -0.17, p < 0.0001), number of unacceptable images (R(2)  = 0.14, p < 0.0001) and number of ultrasound scans performed per year (R(2)  = -0.19, p < 0.0001).

Our results suggest that both processes are clearly related.