The difference between early Down’s syndrome screening and NT is mainly in the following two aspects: first, the means of examination is different, early Down’s syndrome screening is mainly a blood test, while NT test is an ultrasound to measure the thickness of the posterior cervical zona pellucida of the fetus for examination. Secondly, the significance of the test is different. Early Down’s screening is mainly to determine the likelihood of the fetus suffering from trisomy 21, trisomy 18 and other fetal intelligence problems. If the thickness of the nuchal translucency is less than 3mm, which is within the normal range, it means that the patient has fetal neural tube abnormality and the possibility of chromosomal disease is small; if the thickness is more than 3mm, it indicates the presence of chromosomal abnormality or chromosomal disease. If the thickness is more than 3mm, it indicates the possibility of chromosomal abnormality or neural tube malformation, and further screening is needed.