Amniocentesis can be done at 16-22 weeks of pregnancy. The main groups of people to be examined are high-risk pregnant women over 35 years of age, and then patients who have had previous pregnancies with chromosomally abnormal fetuses. There are also people who are at risk of fetal abnormalities such as exposure to toxic substances and viral infections during pregnancy, and those who are at high risk for Down’s syndrome screening. The main reason for choosing this period for the test is that there is more amniotic fluid, and the placenta and fetus are avoided to be injured under ultrasound guidance. After the test, you must pay attention to rest, reasonable diet, take oral fetal preservation drugs under the guidance of the doctor to avoid causing pre-eclampsia, and not to have sex for half a month. The result will come out in about a week. After the operation, you should pay attention to observe the fetal movement and go to the hospital for re-examination after half a month. If you have lower abdominal cramps and bleeding and fever after the puncture, go to the hospital at any time.