The purpose of amniocentesis is twofold: first, to check the fetus for chromosomal abnormalities, which can usually be done in the OB/GYN laboratory; second, to extract amniotic fluid and send it to other departments for certain special tests, such as virus testing, genetic disease testing, genetic metabolic disease screening, etc. Here I will focus on the issues related to karyotyping in obstetrics and gynecology. Karyotype analysis includes both numerical and structural chromosomal abnormalities. However, the problem that most pregnant women want to clarify through amniocentesis is to exclude the abnormalities of trisomy 21, trisomy 18, trisomy 13 or 45-XO. Therefore, based on this purpose, there are currently three main groups of people who need amniocentesis: 1. Advanced maternal age: actual age at the due date ≥ 35 years. 2. High risk for Down’s syndrome screening: the risk threshold used may vary from hospital to hospital, most hospitals in Beijing use 1:380. 3. Adverse birth history: previous history of habitual miscarriage, history of unexplained fetal death in utero, history of delivery of deformed or chromosomally abnormal children, family genetic disorders, etc. If you have any of these problems, you must first consult a professional doctor to see if your problems can definitely be solved through amniocentesis. Some older pregnant women want to have Down’s syndrome screening first, which is not necessary. Because the purpose of Down’s syndrome screening is to screen out high-risk groups, the screening itself is not an accurate result, but only a risk level to inform. And advanced age is already a high-risk group and does not require further screening.