NT, also known as posterior cervical zona pellucida scan, requires ultrasound measurement of the thickest part of the subcutaneous echogenic hyaline layer in the fetal nuchal collar, NT examination needs to pay attention to the following aspects: 1. examination time: NT examination needs to be performed at 11-13 weeks + 6 days of pregnancy, when the reference value of fetal nuchal zona pellucida thickness is more mature; 2. fetal position: NT examination requires the fetal nuchal area to be taken in a natural position in a median sagittal section, if If the fetus is not in a good position during the examination, the accurate result cannot be measured. The fetus can be turned over or moved to the correct position by coughing or walking, or by the doctor gently pressing the abdomen of the pregnant woman during the examination to obtain a satisfactory image; 3. The normal value of NT is <2.5mm in some hospitals and <3.0mm in others, and NT thickening is associated with fetal chromosomal abnormalities and structural malformations and should be further diagnosed prenatally. The NT test results are not definitive, so the NT thickening alone should not be used to terminate the pregnancy.