The NT test, also known as posterior nuchal translucency scan, is an ultrasound test to determine if the fetus has any developmental abnormalities and is mainly used to assess whether the fetus has Down syndrome with a high accuracy rate and does not require blood sampling. If the NT test is performed with blood sampling, it may be combined with Down’s syndrome screening for a definitive diagnosis of the presence of Down’s syndrome. It is currently recommended to do two screening tests for Down’s syndrome, including early pregnancy screening and midtrimester screening, called combined early and midtrimester sequential screening, with a detection rate of up to 85%. NT values are combined with serology for early pregnancy screening to detect risk values for trisomy 21 as well as trisomy 18. If the early pregnancy screening is low risk, it is recommended to continue with midtrimester screening, and if it is borderline or high risk, it is not necessary to continue with midtrimester screening and non-invasive DNA or amniocentesis is recommended. In addition, NT screening is best at the stage of (11-13) weeks + 6 days of pregnancy, while after 12 weeks, the pregnant woman needs to have her blood drawn for the NT screening, which may also be necessary for the construction of the file.