What tests are needed before amniocentesis?

Amniocentesis is actually a method of screening for Down syndrome and other fetal diseases. Before amniocentesis, other examinations are actually needed, such as blood tests for hepatitis B, syphilis, AIDS, etc.

1. Before amniocentesis, blood needs to be drawn for hepatitis B, syphilis, AIDS, and routine blood tests. In addition, an ultrasound examination is required to check the development of the fetus. It is best to do these tests three days before the operation. It is worth mentioning that amniocentesis has certain risks and may cause miscarriage, so you need to stay in bed for 24 hours after the examination.

2. Amniocentesis is a method of prenatal diagnosis. Generally suitable for prenatal diagnosis in mid-pregnancy. Amniotic fluid exists in the amniotic cavity; the fertilized egg forms the amniotic cavity on the seventh day after fertilization and begins to produce amniotic fluid. The amount of amniotic fluid is 50 ml at 12 weeks of pregnancy, 400 ml at 20 weeks, and 1000-1500 ml at 36-38 weeks. The amount of amniotic fluid decreases slightly as the expected date of delivery approaches.

3. The best time to draw amniotic fluid for prenatal diagnosis is between 16 and 20 weeks of pregnancy. Because the fetus is small at this time and there is relatively more amniotic fluid, the fetus floats in the amniotic fluid with a wider amniotic fluid belt around it. It is not easy to injure the fetus when the amniotic fluid is extracted with a needle. Extracting 20 ml of amniotic fluid only accounts for 1/20 to 1/12 of the total amniotic fluid, which will not cause the uterine cavity to suddenly shrink and cause miscarriage. Moreover, the proportion of active cells in the amniotic fluid is the largest during this period, and the cell culture survival rate is high. It can be used for slide preparation, staining, fetal chromosome karyotype analysis, chromosome genetic disease diagnosis and gender determination, and amniotic fluid cell DNA can also be used to diagnose genetic and metabolic diseases.

4. The measurement of alpha-fetoprotein in amniotic fluid can also be used to diagnose open neural tube defects in the fetus. In the late pregnancy, amniocentesis can measure blood type, bilirubin, lecithin, sphingomyelin, placental lactogen, etc., to understand whether there is maternal-fetal blood type incompatibility, hemolysis, fetal lung maturity, skin maturity, placental function, etc.