General examination of amniotic fluid

Amniotic fluid is the liquid in the amniotic cavity of the early embryo. The early pregnancy is mainly the leakage of maternal plasma into the amniotic membrane through the membrane. In the middle stage, fetal urine is the main source. Amniotic fluid has the function of protecting the fetus and protecting the mother during pregnancy. Amniotic fluid specimens are usually obtained by amniocentesis by a general practitioner. Amniocentesis can reflect the growth of the fetus in the uterus, maturity, gender, and diagnosis to help identify certain hereditary diseases. General examination of amniotic fluid includes amniotic fluid volume and amniotic fluid color. Basic Information Specialist classification: maternity check check classification: biochemical examination Applicable gender: whether women are fasting: not fasting Tips: Amniocentesis is usually performed in the second trimester (16-21 weeks of gestation). Normal value Amniotic fluid color Early pregnancy is transparent. Full-term pregnancy is transparent or slightly creamy. Amniotic fluid volume Early pregnancy 0.45 ~ 1.2L (450 ~ 1200ml). Full-term pregnancy 0.50 ~ 1.4L (500 ~ 1400ml). Clinical significance Amniotic fluid volume (1)>1.4L too much amniotic fluid. (2) <0.5L oligohydramnios. Amniotic fluid color (1) Yellow-green or dark green fetal distress (mixed meconium in amniotic fluid). (2) Brown red or brown fetal death. (3) Golden yellow amniotic fluid bilirubin is too high (mother and child blood type incompatibility). (4) Yellow overdue pregnancy with thick brushed, placental function decreased. (5) purulent or odorous intrauterine infection. Precautions Amniocentesis is usually performed in the second trimester (16-21 weeks of gestation). The urine should be drained before surgery, with both hands on the hips and gently turn the waist and abdomen. Then supine, use B-ultrasound to detect the positioning, select the puncture point, and puncture under strict aseptic operation conditions. Generally, about 20 ml of amniotic fluid is taken and placed in a clean and sterilized centrifuge tube for immediate inspection. Inspection process Biochemical and immunological examination Amniotic fluid is a biochemical and immunological examination of serum that is mainly used for the detection of hereditary metabolic diseases. There are currently more than 3,000 known inherited metabolic diseases, and 89 can be used for prenatal diagnosis. These prenatal diagnosis methods for congenital metabolic diseases are mostly complicated. At present, the clinical laboratory is able to carry out some simple methods mainly for the examination of various diseases of the mucopolysaccharide, open neural tube defects and certain enzyme defects. (1) Inspection of mucopolysaccharidosis Mucopolysaccharidosis is caused by a congenital defect of the cell lysosomal acid hydrolase. According to the etiology, the disease can be divided into eight types. China has reported 200 cases from the remaining cases, mainly characterized by severe skeletal malformations, swollen splenomegaly, mental retardation and other malformations. Prenatal diagnosis of mucopolysaccharidosis is the most reliable to determine the specific enzyme activity in cultured amniotic fluid cells, but the experimental requirements are high, which is difficult to carry out in general laboratories. Two simple and practical methods are semi-quantitative determination of toluidine blue and uronic acid. 1. Toluidine blue characterization: The method is the same as the urine mucopolysaccharide test. In normal pregnancy, amniotic fluid can be positive, and negative in the middle and late pregnancy, such as positive, suggest that the fetus suffers from mucopolysaccharidosis. 2. Semi-quantitative determination of uronic acid: The acid mucopolysaccharide in amniotic water reacts with sodium tetraborate sulfuric acid solution to form uronic acid, which reflects the amount of acid glycopolysaccharide per creatinine. As the pregnancy progresses, the uronic acid content gradually decreases, and the reference value of 16-20 weeks of pregnancy is 3.3-7.0 mg/mg Cr. If it is higher than this value, mucopolysaccharide depositional fertilizer disease should be considered. This method has diagnostic significance for other types of mucopolysaccharidosis other than Morguio syndrome. (B) the examination of neural tube defects 1. Alpha-fetoprotein determination of neural tube defects accounted for a large proportion in prenatal diagnosis. The determination of amniotic fluid alpha-fetoprotein is currently a routine method for diagnosing neural tube defects. AFP is mainly synthesized in fetal liver and yolk sac. AFP in sheep comes from fetal urine, and a small part comes from fetal gastrointestinal tract, amnion and chorion cells. AFP in normal pregnancy amniotic fluid was highest at 15 weeks of gestation, up to 40 mg/L, gradually decreased from 20 to 22 weeks, and decreased steadily after 23 weeks. After 32 weeks, it decreased to 25 mg/L and maintained this level until full term. Fetus with open neural tube defects, such as no brain and spina bifida, AFP in fetal blood can infiltrate amniotic fluid from exposed nerve tissue and choroid plexus, making AFP more than 10 times higher than normal. AFP determination in amniotic fluid is a non-specific examination for the diagnosis of fetal neural tube defects. The AFP content in the fetal blood is 150-200 times higher than that of the amniotic fluid. Therefore, the puncture injury and the fetus and the placenta may be falsely elevated. The AFP measurement needs to be diluted 100 times in the mid-pregnancy amniotic fluid, and then determined by serum AFP immunological method. In addition to the detection of amniotic fluid, AFP can also use maternal blood screening to diagnose the open candy through tube malformation accuracy of more than 90%, so it has special diagnostic value. In addition, other fetal malformations such as congenital kidney disease, esophageal atresia, hydrocephalus, appendix malformation, chromosomal abnormalities, diabetes, pre-eclampsia and other reasons caused by insufficient placental function, miscarriage, fetal death, etc., amniotic fluid AFP Can also be raised. 2. Amniotic fluid total cholinesterase assay: commonly used to confirm elevated amniotic fluid AFP levels. The cholinease contained in amniotic fluid is divided into two types: true cholinesterase and pseudocholinesterase, depending on the affinity of acetylcholine. In the early fetal body, CHE has been synthesized. At 12 weeks of gestation, the CHE of the sheep is significantly increased. When the fetal nerve is slightly immature, the CHE from the fetal spinal fluid and blood oozing into the amniotic fluid is more mature. The time is too much, so it can be used for the diagnosis of open-ended neural tube defects as amniotic fluid TCHE. The measurement method is a rate method or an end point method using propionylthiocholine or acetylthio base as a substrate and 5,5-dithiobis as a color developer. 3. Determination of true acetylcholine esterase activity in amniotic fluid The increase of true acetylcholine ester activity in amniotic fluid is highly correlated with fetal open neural tube defects. ACHE qualitative polyacrylamide gel electrophoresis analysis is currently the most commonly used method, especially for neural tube. Diagnosis of malformed suspiciousness. The method firstly separates PCHE and ACHE by PH8.1 electrophoresis, and then incubated with CHE substrate acetyl sulfide low choline and reflecting agent according to the principle of enzymatic reaction, and CHE decomposes the thiobase and copper produced by the substrate. The ionic reaction forms a complex, and a white precipitation line appears in the enzyme zone business. A slow PCHE zone can be seen after normal amniotic fluid electrophoresis, and the fast ACHE zone is extremely small. The ACHE zone of the fast-stroke amniotic fluid was observed in the amniotic fluid, and the ACHE zone disappeared after electrophoresis of the ACHE-specific inhibitor BW284C51. ACHE qualitative electrophoresis must be done with positive and negative controls to ensure that the binding judgment is accurate. The positive rate of screening for non-brain malformation and open-sided spina bifida can reach 99.5%, but the fetus suffers from umbilical hernia. Other severe congenital malformations into the amniotic fluid ACHE can also be positive. Therefore, for the diagnosis conclusion, the decision whether to complete or terminate the pregnancy must be considered in combination with other examinations. (C) examination of pancreatic fibrocystic changes 1. γ-glutamyltransferase assay: GGT activity in normal pregnancy amniotic fluid is highest at 14-15 weeks of gestation, about 10-100 times that of maternal plasma, and then gradually decreases to 30-40 weeks of gestational age, only 1/40 at 15 weeks. The best predictor of early diagnosis of pancreatic fibrosis in GGT was measured at around 15 weeks, with a predictive accuracy of 77-84%. The reason for the decrease in GGT was that the small intestine microvilli enriched with GGT stopped developing or inhibited enzymes. The matter is released into the amniotic fluid. In addition, the fetal staining of the body disease, such as the 21 trisomy or trisomy 18, also significantly decreased GGT. 2. Alkaline phosphatase assay The amniotic fluid ALP has the highest activity around 19 weeks of gestation, then gradually decreases, and the activity drops to the prenatal level after 29 weeks. In the 16-24 weeks of gestation, 3/4 of the amniotic fluid ALP is small intestine type, and 1/4 is liver, bone and kidney type. In the cystic changes of fetal pancreas, the small intestinal ALP is extremely decreased due to abnormal microvilli on the surface of the intestinal mucosa. In addition, it can assist in the diagnosis of a decrease in ALP activity in the 21 trisomy 18 trisomy syndrome. (4) Inspection of stillbirth 1. Determination of creatinine kinase The activity of amniotic fluid CK has nothing to do with gestational age. In normal pregnant women, the serum concentration is about 1/5 or lower, and the main worker is CK-BB. The increase of CK in amniotic fluid mainly comes from the decomposition of skeletal muscle in the dead fetus, so the CK activity is positively correlated with the time of death, and it is elevated by CK-MM. In addition, the CK-BB content of teratoma, abdominal fissure or non-cerebral teratogenic amniotic fluid can also be increased. 2. Lactate dehydrogenase determination of LD activity in dead fetus amniotic fluid increased significantly, but due to intrauterine tissue damage, amniotic fluid contaminated by red blood cells can cause amniotic fluid LD increased, so the specificity is not strong. Not suitable for the crowd Generally there are no people who are not suitable. Adverse reactions and risks Generally no adverse reactions.