The 12-week NT test is a mandatory test during pregnancy, which is mainly to check the thickness of the posterior nuchal translucency band and to preliminarily rule out fetal malformations. NT examination is one of the necessary checkups during pregnancy, the posterior nuchal translucency zone is most obvious in 11-13 weeks of pregnancy, and gradually fades after 14 weeks, i.e., it is best to check it at 11-13 weeks +6 weeks of pregnancy, mainly through ultrasound to detect the thickness of the fetal posterior nuchal translucency zone. It is important for screening fetal chromosomal abnormalities. Under normal circumstances, the NT value should be below 2.5mm. If the fetus suffers from chromosomal diseases, gene-based diseases, or combined with a more serious malformation fetus, a significant thickening of NT may occur when the NT examination is performed at 12 weeks of pregnancy. Therefore, once the NT value is found to be greater than 2.5mm, it is recommended that the pregnant woman should consult a doctor in time for further examination to rule out the possibility of chromosomal diseases in the fetus.