NT examines the thickness of the nuchal translucency, which is the thickness of fluid accumulation in the subcutaneous tissue at the posterior part of the fetal neck. The degree of fluid accumulation in this area can reflect the degree of fetal metabolism, and can assess whether the fetus has chromosomal abnormalities resulting in malformations, such as spinal malformations, congenital heart disease, structural heart malformations, etc., can be evaluated when testing the thickness of the nuchal translucency layer, screening out fetuses with abnormal indicators and requiring further examination; it can also determine whether the fetus has Down syndrome, which belongs to early Down syndrome screening It can also determine whether the fetus has Down’s syndrome, which is an early screening test. The NT test can be done from the abdomen or from the vagina without any special requirements, no need to fast or hold urine. 2. Once this time has passed, the accuracy may decrease significantly. Therefore, it is important to have the test within the time frame specified by the doctor, especially for pregnant women who have irregular periods, it is best to have an ultrasound to determine the gestational week in the early stages so as not to miss the NT test.