What Is an Amniotic Fluid Test?
The examination of amniotic fluid is mostly carried out during 16-20 weeks of pregnancy, and amniotic fluid is used for examination. Examination items include cell culture, sex chromosome identification, karyotype analysis, amniotic fluid alpha-fetoprotein determination, biochemical examination of amniotic fluid, etc. to determine the maturity and health of the fetus, and to diagnose whether the fetus is normal or has certain genetic diseases.
Amniotic fluid check
- Amniotic fluid tests are mostly performed during 16-20 weeks of pregnancy
- The amniotic fluid volume was about 250 ml at 16 weeks of gestation and peaked at 34 weeks . About 1000 ml (800-1200 ml) in the third trimester of pregnancy gradually decreases from the last 2-4 weeks of pregnancy,
- Pregnant women who have had women with open neural tube abnormalities: Pregnant women who have had children with brainless or spina bifida, the probability of the next child being born is 5%. Pregnant women who have given birth to a child with an autosomal recessive metabolic disease: These women are 25% more likely to have the same disease in the next child. Pregnant women with a history of exposure to causative factors: Exposure to certain physical factors that affect chromosomal aberrations, chemicals, drugs, and pregnant women with a history of viral infection. Pregnant
- Congenital malformation
- By measuring alpha-fetoprotein in amniotic fluid, we can know whether the fetus is deformed. Alpha-fetoprotein is a unique protein in the fetal period, and some congenital malformations can increase the alpha-fetoprotein content in amniotic fluid.
- Congenital metabolic defect
- Causes of Amniotic Fluid Check
- 1. Pregnant women with a family history of X-linked genetic diseases.
- 2. Marriage between close relatives and pregnant women who have had children with congenital malformations.
- 3. Pregnant women who need to know the sex of the fetus (
- Amniotic Fluid Index (AFI): The umbilical horizontal line and ventral white line are used as marks to divide the right angle of the uterus into four quadrants. The vertical line of the largest amniotic fluid in each quadrant is measured. The sum of the four is the amniotic fluid index. Note when measuring AFI: If the sheep pond is located on both sides of the marking line, only the diameter line on one side is measured.
- Amniocentesis
- 98-99% of the amniotic fluid is water and 1-2% is solute. Solutes are half organic and half are inorganic salts. There are also very few cells.
- (I) Organic ingredients Glucose: The glucose content in the number one water is lower than that in the mother's serum, about 2.02-2.76mmol / L. After 37 weeks of pregnancy due to placental penetration
- Fetal maturity test
- The monitoring of fetal maturity is an important basis for determining a reasonable divorce time and treatment policy for high-risk pregnancy. It is mainly to observe whether the fetal organ function is well developed through the fluctuation of a substance in the amniotic fluid.
- Prenatal diagnosis of congenital hereditary diseases
- Congenital diseases include hereditary diseases
- Prediction of fetal blood type
- ABH (O) blood group substance exists in amniotic fluid, so the blood group of the fetus can be predicted during pregnancy, in order to perform perinatal monitoring, treatment and preparation for the rescue of newborns with maternal fetal blood group incompatibility.
- ABH secretory blood type
- This test is designed based on the principle that blood group substances secreted in sheep can neutralize the antibodies in the corresponding antiserum. Mix the amniotic fluid with 0.2 ml of the optimal dilution of anti-A, anti-B, and anti-H serum 0.2 ml, and after Feng Feng acts for 10 minutes, the blood group substances will completely neutralize the antibodies, and then add the corresponding 2% standard A 0.2ml each of type B, type B, and type O erythrocyte suspensions, mix well. Set at room temperature for 30 min, and centrifuge at low speed for 1 minute to observe whether there is agglutination. The results are judged in Table 18-1.
- Table 18-1 Judgment of blood type of amniotic fluid
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- The most critical part of this test is to choose the optimal dilution of the antiserum. That is to say, the selection of antiserum and 2% standard red blood cell suspension can produce the highest dilution of 4+ agglutination, so that after the addition of amniotic fluid, the corresponding antibody will be neutralized and no 4+ agglutination will occur. Normally, 0.2ml of antiserum is diluted 1: 1-1: 256 times with normal saline, and 2% of standard red blood cells of type A, B, and O are added to 0.2ml, and the mixture is allowed to stand at room temperature for 1 hour to observe the results. The highest dilution of 4+ clot was determined as the optimal dilution. In the experiment, care should be taken to control the temperature, so as not to cause the wrong judgment due to the incomplete absorption of the agglutinin in the antiserum.
- ABH (O) blood type
- The measurement of ABH blood group substances in amniotic fluid cannot predict the blood group of non-secretory fetuses. It is known that the N-acetylgalactosyltransferase produced by the A gene can link the N-acetylgalactosyl galactose to the galactose at the end of the H substance to form a blood group A substance. The D-galactosyltransferase produced by the B gene converts the D -Galactose is linked to galactose at the end of substance H, forming a blood group B substance. When a sugar donor, divalent manganese ions and O-type red blood cells are co-incubated, transferase in amniotic fluid can combine substance A or B on the red blood cell membrane, and the blood type of the buried secretory fetus can be detected by blood group determination. At this time, the identification of non-secretory fetal blood types of pregnant women with a history of severe ABO alloimmunization provides the possibility of prenatal diagnosis of genetic diseases located at the ABO gene site, regardless of whether the fetus is secreted. .