NT test is an ultrasound examination of the thickness of the posterior nuchal translucency layer of the fetus at (11-13) weeks + 6 days of pregnancy. Fetal NT thickening is defined as a fetal posterior nuchal translucency layer thickness exceeding the normal value, which needs to be alerted to related diseases caused by chromosomal and genetic abnormalities. Usually, NT value > 3.0mm is considered as thickening and increased NT value indicates the possibility of chromosomal abnormalities in the fetus, such as trisomy 21, trisomy 18 and trisomy 13. Besides, NT values are also associated with congenital heart disease, cervical hydatid cystic tumor, and non-immune edema. Therefore, when thickening of the hyaline layer is detected, pregnant women should undergo genetic counseling and prenatal diagnosis under the guidance of a physician. It is recommended to check the fetal karyotype, such as non-invasive DNA testing, chorionic villus aspiration test or amniocentesis. For those with normal karyotype, close observation is needed to rule out congenital structural heart abnormalities. If chromosomal abnormalities are present, the fetus may suffer from pre-eclampsia, embryonic arrest during pregnancy, or fetal development may be delayed during pregnancy, or it may be born with congenital stupidity, mental retardation, weak speech, or low IQ, which may affect the family and the individual.