Uncertainty in nuchal translucency reference ranges at 11–14weeks of gestation – comparison to Swedish centiles

Objective. To generate a regression equation for the nuchal translucency (NT) median for the Swedish population and compare this with other median values. Setting. Eight Swedish hospitals. Sample. The data set included 20 887 unaffected fetuses. Methods. Calculation and generation of an NT centile chart for the Swedish population. Results. The NT centiles for crown-rump length (CRL) from 45 to 84mm were calculated and compared with the medians from Glasgow, from the Fetal Medicine Foundation (FMF, London, UK; FMF-original) and those published recently (FMF-new). The NT medians cease to increase at CRLs between 70 and 75mm. The Swedish, FMF-new and Glasgow medians followed the same pattern, but the Glasgow NT median curve was systematically lower by around 20%. Swedish, FMF-new and Glasgow medians differed in shape from the FMF-original medians, which continuously increase throughout the whole range of CRLs. Conclusions. Our results demonstrate that there are substantial differences in the NT medians and centiles between countries.