Monitoring quality control of nuchal translucency

Nuchal translucency is the single most discriminatory marker for screening Down syndrome. When this marker is combined with concurrent maternal serum markers, the model-predicted performance is greater than for all second-trimester serum-only combinations. However, quality results for the marker are more difficult to achieve than for serum markers. Monitoring of images and proper training are essential, but the ongoing use of epidemiologic indicators is the only way to assure quality. The positive rate in the screened population may indicate a problem, but the average multiple of the normal median values and the standard deviation of the logarithm (base 10) of these values are the key indicators for the markers. If there is a 10% shift in the median or a 0.02 change in the standard deviation, the results will be compromised.