NT is normal, generally over 35 years old pregnant women are recommended to do non-invasive DNA testing, can be blood or amniocentesis, if not more than 35 years old can do Down syndrome screening can also do non-invasive DNA testing, if the results of the screening can be normal can not be further examination, if the results of the screening results of the medium-risk or high-risk need to do further non-invasive DNA or amniocentesis. Early Down’s syndrome screening consists of 2 tests, ultrasound for fetal nuchal translucency (NT) in early pregnancy and mid-pregnancy screening for Down’s syndrome and non-invasive DNA and amniocentesis to comprehensively assess the risk of Down’s syndrome screening. Only amniocentesis has a 100% diagnostic rate for Down’s syndrome, so every test other than amniocentesis that is abnormal requires further testing.