Sonographically measured nuchal skinfold thickness as a screening tool for Down syndrome: results of a prospective clinical trial.

Second-trimester sonographic measurement of nuchal skinfold thickness has been proposed as a potential screening tool for Down syndrome detection. The feasibility of this technique was tested in a prospective study of 3338 consecutive pregnancies at 14-21 weeks' gestation. A nuchal skinfold thickness of 6 mm or greater was identified in 47 fetuses (1.4%), 12 of whom proved subsequently by either amniocentesis or postnatal follow-up to have Down syndrome. The sensitivity of nuchal skinfold thickness for Down syndrome detection was 75% (12 of 16 cases). When adjusted for the incidence of Down syndrome in the general population (one in 710 births), the positive predictive value of nuchal skinfold thickness for Down syndrome detection was one in 13. The observed sensitivity, false-positive rate, and predictive value suggest that amniocentesis should be offered when a nuchal skinfold thickness of 6 mm or greater is observed between 14-21 weeks' gestation.