NT test is the nuchal translucency scan, which is to check the thickness of fluid accumulation in the subcutaneous tissue at the back of the fetal neck. NT test is usually performed at 11-13 weeks + 6 days of pregnancy, normally, NT thickness will increase with the growth of the fetus, but will not exceed 3mm, if it exceeds 3mm, it also means that the fetal body circulation resistance increases and the lymphatic fluid return obstruction accumulates in the fetal neck, it will lead to the fetal nuchal The thickening of the zona pellucida suggests the possibility of chromosomal abnormalities, fetal structural malformations, and monogenic diseases, but the simple NT thickness value does not confirm the diagnosis, and further examination is needed, specific analysis: 1. chromosomal abnormalities: including chromosomal structure and number abnormalities, common fetal chromosomal abnormalities, such as trisomy 21, trisomy 18, trisomy 13 and DiGeorge syndrome; 2, fetal structural abnormalities: such as congenital heart disease, abnormal development of the lymphatic system and other abnormalities, such as abnormal development of the skeletal system, abdominal wall defects, diaphragmatic hernia, etc., will also suggest NT thickening, the heavier the degree of thickening, the greater the chance of suggesting the presence of the disease, but further examination is still needed to confirm the diagnosis; 3, monogenic diseases: such as Noonan syndrome, etc., will also appear NT thickening. Therefore, for pregnant women with thickened NT, invasive prenatal diagnosis, such as chorionic villus aspiration or amniocentesis for fetal chromosomes and genes, is recommended. If the pregnant woman is concerned about the risk of a puncture, she can also choose non-invasive DNA testing, but it should be noted that non-invasive DNA is only a screening test, with false positives and false negatives, and further amniocentesis is still needed for high risk of non-invasive DNA. If the amniocentesis results suggest abnormalities, genetic counseling should be performed to determine if termination of pregnancy is necessary. In addition, attention should be paid to the screening of fetal structural malformations in the middle of pregnancy, and fetal echocardiography is recommended for NT ≥ 3 mm.