Cut-off criteria for second-trimester nuchal skinfold thickness for prenatal detection of Down syndrome in a Thai population

Abstract

Objective: To evaluate the use of progressive cut-offs for nuchal skinfold thickness with advancing gestational age and the commonly applied cut-off method (≥6 mm) for prenatal detection of Down syndrome in a Thai population. Method: A prospective study was performed by experienced perinatologists on 2150 women undergoing second-trimester amniocentesis for the indications of advanced maternal age and past history of chromosomal abnormality. Reference ranges were established for nuchal skinfold thickness from the 16th to the 24th week, using either gestational-specific centiles or the parametric method. Assaying different cut-off criteria for both centile and the parametric methods were calculated and then compared with the commonly applied cut-off level (≥6 mm.). Results: There were 2114 chromosomally normal pregnancies, 19 fetuses with Down syndrome (1:113), and 17 other chromosome abnormalities. In fetuses with normal karyotype the nuchal skinfold thickness increased with advancing gestational age [NF (mm)=−0.502+0.212 GA (week), r=0.36, P<0.001]. The sensitivities of an abnormal nuchal skinfold thickness using different cut-off criteria for detecting Down syndrome were low (5.3–26.3%) with the false positive rates ranging from 2.5 to 16.5%. Conclusions: In this study, measurement of second-trimester nuchal skinfold thickness was a poor and unreliable screening test for fetal Down syndrome in a Thai population.