Amniotic fluid is the urine of the fetus. A little bit of fetal urine is extracted through amniocentesis and cells are isolated from it for in vitro culture, which can diagnose fetal chromosomal abnormalities such as trisomy 21, thalassemia, albinism, pseudohypertrophic muscular dystrophy, deafness, spinal muscular atrophy and other diseases. Which pregnant women need to have amniotic fluid examination? 1.Pregnant women who are 35 years old or older at the time of delivery; 2.Prenatal screening indicates high risk of fetal malformation; 3.Ultrasound abnormal fetal anomaly; 4.Have given birth to a child with serious hereditary disease or serious defects; 5.Chromosomal abnormality, congenital malformation or carrier of disease-causing gene in one of the spouses; 6.Exposure to drugs or rays that may cause fetal malformation during pregnancy; 7.Definite genetic disease Family history; 8. Abnormalities of placenta, amniotic fluid and umbilical cord; 9. History of bad pregnancy and delivery, such as history of fetal abortion, stillbirth, stillbirth, neonatal death, etc.; 10. Mother suffering from certain diseases that may lead to fetal malformation. How is amniotic fluid examination done? The extraction of amniotic fluid is performed under ultrasound guidance. The whole puncture process takes about 2 minutes, including pre-operative procedures such as listening to the fetal heartbeat, positioning, disinfection, spreading sterile sheets, puncture, and wound treatment. No anesthetic is needed and the pain level is similar to a blood test or a muscle injection. Timing: After 18 weeks (above 42mm biparietal diameter) and up to 24 weeks is the best time for amniotic fluid chromosome culture. Amniotic fluid testing can also be performed after 26 weeks of gestation to check for chromosomal whole genome microarrays. In the case of paternity test patients, the amniotic fluid test can be performed earlier than 16 weeks. Things to prepare for the amniotic fluid test: a copy of your ID card at the time of appointment, four viral tests (Hepatitis B, Hepatitis C, Syphilis, HIV) within 3 months of pregnancy, blood type ABO+RH (for life), ECG (this test is required if the pregnant woman has a history of heart disease), routine blood (within 1 week), ultrasound (within 2 weeks).