After thirteen weeks of pregnancy, pregnant women need to do NT test, prenatal screening or prenatal diagnosis, screening for fetal structural abnormalities. 1. NT examination: NT refers to the thickness of fetal nuchal translucency, which is a screening method to detect chromosomal abnormalities in early pregnancy. It should be tested at 11~13+6 weeks of pregnancy in accordance with the doctor’s prescription, and the normal value is ≤2.5mm. 2. Prenatal screening or prenatal diagnosis: by screening the risk of pregnancy, for the medium and low risk groups, we should carry out Down’s syndrome screening, non-invasive prenatal examination technology and other prenatal examination means as prescribed by the doctor in the 15th to 20th week of pregnancy. For high-risk groups, amniocentesis and other prenatal diagnostic methods should be performed at 16~22 weeks of gestation as prescribed by the doctor. 3. Fetal structural malformation screening: During 20~24 weeks of pregnancy, ultrasonography is needed to systematically screen the fetal organs to detect fetal structural malformations, such as anencephaly, severe cerebral bulging, and severe thoracic and abdominal wall defects, etc. In addition, in clinical practice, ultrasonography is needed at 13 weeks of pregnancy. In addition, in the clinic, you need to consult with a specialized physician to find out what tests you need to do at 13 weeks of pregnancy.