Fetal NT thickening carries a risk of fetal chromosomal abnormalities or malformations, with specific risk indicators related to NT thickness and the presence of other abnormalities in combination. The NT test is performed by ultrasound to measure the fetal nuchal translucency thickness between 11 weeks and 13+6 days of gestation, with a head and hip diameter of 45-84 mm, to see if the fetus is at risk for chromosomal abnormalities.The NT test is a non-invasive test that is not affected by eating. NT is a strong marker of aneuploidy and is normal up to 3mm, greater than 3mm, 90% are normal fetuses, 10% are abnormal fetuses and greater than 6mm, 90% are abnormal fetuses. If the NT is thickened, further non-invasive prenatal screening or prenatal diagnosis is needed to rule out fetal chromosomal abnormalities.