The NT test is an abdominal ultrasound that is not performed as a negative ultrasound. The NT test is to check the thickness of the posterior nuchal translucency layer of the fetus. It is necessary to do an abdominal ultrasound because of the limitations of the ultrasound at this time. This test can be done between 11 and 13+6 weeks of pregnancy. The normal value is within 3mm. If it is more than 3mm it may be due to chromosomal abnormality of the fetus or malformation of the heart development, which is due to lymphatic reflux disorder, so further examination is necessary. A non-invasive DNA test or an amniocentesis test is required. The NT thickening can only indicate a significant increase in the incidence of fetal developmental malformations, but it cannot confirm the diagnosis.