NT examination is a kind of B-ultrasound examination, that is, NT examination can be carried out by using B-ultrasound or color ultrasound, while B-ultrasound is a routine examination, in addition to NT, other conditions of pregnant women and fetuses can also be examined, the difference is mainly as follows: 1. Usually, the NT examination is done through ultrasound or color ultrasound to check the thickness of the nuchal translucency to determine whether the fetus has structural malformations, if the value is >2.5mm, there may be a risk of Down’s syndrome and further examination through non-invasive DNA or amniocentesis is needed; while early ultrasound examination can clarify whether the pregnant woman has a gestational sac, fetal heart, fetal bud, etc., and the size of the fetus, fetal position, the presence of fetal developmental malformations and placental position can also be checked through ultrasound at 28 weeks of pregnancy. In the 28th week of pregnancy, ultrasound can also be used to check the fetal size, fetal position, fetal malformation, placenta position and maternal amniotic fluid index. However, ultrasound examination can also be used to check other gynecological diseases and is not limited to pregnancy, such as pelvic inflammatory disease, uterine tumors, endometrial diseases, etc. Ultrasound can be used; 2. Examination time: NT examination usually has a time limit, mostly at 11-13 weeks + 6 days of pregnancy, while the first ultrasound examination of pregnant women is at 40-60 days of pregnancy, and the whole pregnancy is usually examined 5-6 times.