NT ultrasonography mainly measures the thickness of the nuchal translucency layer of the fetus, generally, the thickness will be less than 2.5 mm. When the NT examination is above 2.5 mm, it suggests that the abnormal thickening of the NT of the fetus may be caused by fetal soft tissue edema, or it may be due to fetal chromosomal abnormalities, cardiac abnormalities, and the possibility of various comprehensive spontaneous abortions will increase. Relatively speaking, if the thickness of the nuchal translucency exceeds 2.5 mm, the risk of chromosomal abnormalities in the child will increase. It is recommended to perform chromosomal examination of the fetus through amniocentesis or chorionic villus sampling, and if the chromosomal examination is confirmed to be normal, another ultrasound examination will be performed at around 18 weeks to evaluate the heart as well as other structures with abnormalities.