The nuchal fold is a measurement taken at the back of the fetal neck during prenatal ultrasound, typically performed in the second trimester between 15 and 20 weeks of gestation. A thickened nuchal fold, typically defined as greater than 6 millimeters, is considered a soft marker for chromosomal abnormalities, particularly Down syndrome (Trisomy 21). The nuchal fold measurement is typically performed in the transverse plane at the level of the cerebellum. While a thickened nuchal fold increases the risk of chromosomal abnormality, many fetuses with increased nuchal fold thickness have normal chromosomes and are born without abnormality. The nuchal fold measurement is most appropriately used as one component of a comprehensive screening approach that includes other markers.
Sonography Term