Nuchal index: a gestational age independent ultrasound marker for the detection of Down syndrome

Abstract

Nuchal Index (NIx) can be assumed to be constant between 14 + 0 and 22 + 6. Using a threshold of 11.0, the sensitivity for any Down syndrome (DS) fetus was 62% (32/52) with a specificity of 96% (False positive rate = 4%). Even when obvious fetal conditions that can cause an increase in NIx are excluded, the sensitivity remains acceptable at 50%. NIx appears to be a useful, gestational age independent ultrasound marker for Down syndrome.