When it comes to Down screening, we are all no strangers. With the popularity of Down screening, we all need to have a clearer understanding and use of it. The following is a summary of what we know after checking some of the information! Down’s syndrome and neural tube defects are two of the conditions recommended by the Ministry of Health for prenatal screening nationwide. Recent studies have shown that 80% of children with trisomy 21 have mothers under the age of 35. The current strategy of prenatal screening is to routinely perform serological screening for Down syndrome and neural tube defects, regardless of the age of the pregnant woman and her history of abnormal pregnancies, and to perform prenatal diagnosis if positive, in order to minimize the rate of birth defects. Although risk factors for Down syndrome increase with maternal age greater than 35 years (as maternal age increases, the greater the likelihood of chromosomal non-segregation during meiosis and the tendency to deliver chromosomally abnormal fetuses), most Down syndrome infants are born to mothers younger than 35 years of age and, moreover, 70% of Down syndrome infants are not determined by maternal age. The current practice in the United States is to recommend prenatal screening with maternal blood for those under 35 years of age, and direct chorionic villus or amniotic fluid sampling for prenatal diagnosis for those over 35 years of age. In China, it is already routinely done free of charge in some areas, but it should usually be done for pregnant women under the age of 18 and over the age of 35. When to perform Down screening and how to interpret a positive result: For pregnant women within 14-20 weeks of pregnancy, with informed consent, 2-3 ml of fasting venous blood is drawn, injected into a dry tube without anticoagulant, centrifuged immediately, and the supernatant is transferred into a centrifuge tube and stored airtight and frozen at -20°C for testing. At the same time, detailed information on the last menstrual period, date of birth, weight, type 1 diabetes, whether she smokes, number of fetuses, adverse pregnancy and delivery history, and contact information are collected. Because the risk value of Down screening is calculated by special software according to a certain formula after accepting the age, gestational week and laboratory results, the accuracy of the above information collected is very critical, especially the gestational week, which is usually determined by first doing an ultrasound to see the fetal biparietal diameter. In addition, the first ultrasound measurement of the size of the gestational sac or germ, against the early pregnancy days table, the smaller the germ the more accurate, up and down generally only a day or two (like a two-year-old child, grows about the same height, grows to 20 years old, the age is the same, the height is very different). There is also a more accurate way to project the gestational week is part of the planned pregnancy pregnant women, can remember the day of conception, the day or the next day, of course, to add 2 weeks is what we often call the gestational week. Down’s syndrome screening is divided into early screening and mid-term screening, early pregnancy for NT + PAPP-A or PAPP-A + β-HCG, mid-term pregnancy AFP + β-HCG + free E3 + inhibinA, (now most hospitals apply the dual test of the test, that is, AFP HCG, there is also the application of triple, that is, AFP HCG uE2, two-phase results vary greatly, but also There is the sample size within the software also determines the sensitivity, positive detection rate, true positive rate, etc. Therefore, when the first test is positive, it is recommended to re-evaluate the above to determine the results.) If early screening is high risk, midterm screening is required; if still high risk, prenatal diagnosis is required to check fetal chromosomes; if midtrimester screening is low risk, only fetal genetics ultrasound screening is required; if abnormal ultrasound soft indicators are found, prenatal diagnosis is required to check fetal chromosomes; if no abnormal ultrasound is seen, only regular obstetric examination is required. Amniocentesis: Amniocentesis is considered in three aspects: 1, is a large enough pool of amniotic fluid, the fetus is safer when punctured; 2, can obtain a sufficient amount of easily cultured fetal exfoliated cells to ensure chromosomal analysis (some data show that to perform amniotic fluid cell culture, usually 16-17 weeks of amniotic fluid, the success rate is only 90% , the best time is about 20W, the highest success rate, 98%) The best time is around 20W, which has the highest success rate of 98%); 3. Under the premise of safety, early diagnosis can be made and early treatment can be done, which also helps to relieve the anxiety of pregnant women waiting. In fact, nowadays, amniocentesis is performed under ultrasound monitoring, which is safer for both the fetus and the adult. Other related awareness: 1. The popularity of Down screening is not because it has such a high false positive rate, but because Down’s syndrome is such a serious burden on families and society. And there is not a better solution to this problem than the current means. The fact that the fetal abnormality does not happen to you then even if it is one in two has nothing to do with you, but once it happens to you, it is 100 percent. 2, in vitro fertilization need to do Down screening: there are reports, in vitro fertilization compared with natural pregnancy, natural group deformity rate 2.3%, in vitro fertilization group 2,5%, no statistical difference, so they need to do. However, if the fertility center has already done more accurate fluorescence in situ hybridization testing during the pre-genetic diagnosis when doing IVF, which includes 13, 18, 21, X and Y of Down’s syndrome screening, there is no need to do Down’s syndrome screening again. 3, as mentioned above, the risk value is entered into the data software to automatically calculate the generation, and many hospitals are still lacking multi-child Down screening calculation software, if the method and standard of a single child is not much meaningful. 4, the same serum, using different testing methods and different manufacturers of reagents, the actual quantitative value will be different. There is no universal database that can be applied to different reagents. 5, The role of NT (posterior nuchal translucency) test performed at 10+3 weeks – 13+6 weeks (top hip length approximately 36 – 86 mm) in screening for Down’s syndrome has been increased. The sensitivity of NT thickening in the diagnosis of trisomy 21, trisomy 18, and trisomy 13 is about 70% . Therefore, high risk for trisomy 18 or trisomy 21 requires amniocentesis or cord blood sampling. For pregnant women with a high risk of NTD, they are usually allowed to increase the number of ultrasounds during pregnancy, and to be screened by ultrasound or MRI, and less amniocentesis is done for simple high risk of NTD. 6, Down’s syndrome screening is a probability test, whether high risk or low risk can not be considered a certain occurrence or a certain non-occurrence. Of course, to be sure, amniocentesis chromosome test is the most direct and accurate