Sonographic measurement of nuchal skinfold thickness for detection of Down syndrome in the second-trimester fetus: a multicenter prospective study. The AFDPHE Study Group. Association Française pour le Dépistage et la Prévention des Handicaps de l'Enfant.

OBJECTIVE: To determine the sensitivity and specificity of soft-tissue nuchal-fold measurement in the second-trimester fetus for the detection of trisomy 21.
METHOD: Thirty-six investigators in 12 centers measured nuchal skinfold thickness in 3308 fetuses of 14-24 weeks' gestation. All mothers were referred for amniocentesis because of age, history of genetic disorder, or laboratory findings. Those referred with an ultrasound indication for amniocentesis, including nuchal-fold thickening, were excluded.
RESULTS: Overall, nuchal skinfold was 6 mm or more in 8.5% of chromosomally normal fetuses and in 38% of those with trisomy 21. A false-positive rate below 5% was obtained by 81% of the investigators. Raising the cutoff of normality to 7 mm after 18 weeks' gestation improved specificity.
CONCLUSION: Although the diagnostic value of this sign in skilled hands could allow its use as an indication for genetic amniocentesis at the second trimester, the method does not appear suitable for population screening because of the high variability in the results among the investigators.