Impact of quality of nuchal translucency measurements on detection rates of trisomies 13 and 18

Objective: To determine the relative contribution of nuchal translucency (NT) to the biochemical detection rates of combined screening for trisomies 13 and 18 in two healthcare systems practicing different quality-control systems of nuchal measurement. Methods: De-identified data collected from the Fetal Medicine Foundation in the United Kingdom and laboratory data from NTD laboratories in the United States were compared for detection rate and false-positive rate (FPR) for combined trisomies 13 and 18 screening and were subcategorized by biochemical only and biochemistry combined with NT measurement. Results: US and UK biochemical detection rates were virtually identical: 83% for a FPR of 1.8%. When NT measurement was added, the US rate increased to 88% for a 0.7 FPR, but in the UK the rate increased to 94% for a FPR of 0.3%. The mean NT was 1.69 mm in the US and 2.82 mm in the UK. Conclusions: NT measurement as practiced in the UK system with tight quality control significantly increased the detection rate and significantly reduced the FPR of combined screening for trisomies 13 and 18, when compared to the US with apparently less rigid quality control.