After pregnancy, every pregnant woman will encounter a knot is the screening and diagnosis of Down syndrome, which is also one of the biggest knot during pregnancy, often encountered in the clinic, some mothers-to-be and their husbands discuss this for a long time or still can not make up their minds. The more choices there are, the more complications there are. There are early pregnancy screening, mid-pregnancy screening, combined early and mid-pregnancy screening, duplex, triple or quadruplex screening, and there are also various combinations of Integrated, Continuous Combined, Contingent, and Sequential in the early and mid-pregnancy screening program, and in addition to the serologic indicators, ultrasound can also be added to the soft indicators. The screening program is now adding a new screening test for N. Nowadays, there is also the screening test NIPT (Non-Invasive Fetal DNA Test), and of course, amniocentesis can also be chosen directly. Each method has its own corresponding indications, contraindications, as well as advantages and disadvantages, no method is perfect, so there will be tangled, so there will be obstacles to choice. In order to minimize the obstacles to choice, the comparison of “Down screening”, “non-invasive” and “amniocentesis” is as follows, for reference only. If you are still hesitant after reading this article, you are basically not far from the “choice barrier”. How to deal with “choice disorder”? Please refer to my previous article “Pregnancy and Childbirth – Choice Disorder”. Down’s syndrome screening The so-called Down’s syndrome screening is a procedure in which the mother’s peripheral blood is drawn during early and middle pregnancy to measure the appropriate biochemical markers, and the risk of chromosomal abnormality in the fetus is calculated by the professional screening software after combining the week of gestation, the mother’s age, and her weight. In the Down’s syndrome screening program, there is a serum only program and a combined program of serum screening and ultrasound soft markers. For example, “Early Down” involves taking a sample of the mother’s peripheral blood during early pregnancy to determine the appropriate markers, and then measuring the fetus’s NT (nuchal translucency) to calculate the risk of chromosomal abnormalities in the fetus. If the risk exceeds a set cut-off value (e.g. 1/270), it is defined as high risk and your doctor will usually recommend amniocentesis. Low-risk amniocentesis is generally not necessary, but please note that low-risk does not mean “no risk”, it just means that the risk of chromosomal abnormality in the fetus is less than that in the general population, and the fetus is still at a certain risk of chromosomal abnormality, but it is just a smaller risk. Advantages: (1) only need to extract the peripheral blood of pregnant women, no need to puncture, no trauma to the fetus and pregnant women; (2) low price, generally 150-300 yuan; (3) certain serological indicators of pregnant women can not only predict the risk of trisomy 21, trisomy 18, trisomy 13 and neural tube defects, but also predict the risk of sex chromosome abnormality and structural abnormality, as well as some pregnancy complications (such as pre-eclampsia) early prediction. It is also valuable for the early prediction of sex chromosome and structural abnormalities, and certain pregnancy complications (e.g., preeclampsia). Limitations: (1) Strict requirements on gestational weeks: 6 days in 11-13 weeks for the Early Down, 14-20 weeks for the Middle Down; (2) Calculation of the risk of 21-trisomy, 18-trisomy, 13-trisomy, and neural tube defects only, and no specific risk values can be given for other chromosome numbers and structural abnormalities; (3) Expected chromosomal abnormality detection rate of 60-90%, with false positive rates of 3, 5-8%, and 4%; (4) The risk of chromosomal abnormalities is not known. (3) The expected detection rate of chromosomal abnormalities is 60-90%, and the false-positive rate is 3,5-8% (varying according to different screening strategies); (4) Screening is not the same as a definite diagnosis, if the screening result suggests a high risk, it is necessary to carry out further prenatal diagnosis; if it suggests a low risk, it does not mean that the fetus is completely normal; Indications for the early detection of Down’s syndrome: All pregnant women who are pregnant with a single fetus or twins are eligible to undergo the early detection. However, in the case of multiple pregnancies (three or more pregnancies) or multiple pregnancies where one fetus is stillborn in utero, NT is feasible at this time, but serologic screening is not done. Early detection is also encouraged for women of advanced maternal age, as the significance of NT testing is not only to assess the risk of chromosomal abnormalities, but also to assess the risk of large structural malformations (e.g., cardiac malformations, septal hernias, etc.), genetic syndromes, etc., in the fetus. However, it is important to note that screening is not diagnostic, and that prenatal diagnosis should be considered for women of advanced maternal age, even if they have a low risk of early Down’s syndrome. Indications: Pregnant women with a singleton pregnancy who are less than 35 years of age (the age of the mother at the time of the expected date of delivery). Non-invasive fetal chromosome aneuploidy testing (NIPT) NIPT is performed by collecting peripheral blood of pregnant women, extracting free DNA from the fetus, and using new generation of high-throughput sequencing combined with bioinformatics analysis to derive the risk rate of chromosome aneuploidy disease in the fetus. Advantages: (1) only need to extract the peripheral blood of pregnant women, no need to puncture, no trauma to the fetus and pregnant women; (2) the test can be performed in a wide range of gestational weeks: 12-24 weeks. (3) The expected detection rate is much higher than that of Down’s syndrome screening: the detection rate of trisomy 21, trisomy 18 and trisomy 13 are all higher than 99%, and the false positive rate is lower than 1%, usually around 0.05%, which is an “advanced screening”. Limitations: (1) only for the three chromosomal disorders of trisomy 21, trisomy 18 and trisomy 13; (2) the number of other chromosomal abnormalities and chromosomal chimerism, translocation and other structural anomalies can not be diagnosed; (3) the price of 2,000-3,000 yuan, which is 10 times more than the Down’s syndrome screening, as a means of screening, the price is relatively expensive. (4) Although the detection rate is very high, it is still a technical means of prenatal screening and cannot be used as the final prenatal diagnosis. Indications: Prenatal screening (including serum screening, or ultrasound screening for genetic markers) critical high-risk pregnant women (such as the risk rate of 1/270-1/1000); contraindications to interventional prenatal diagnosis (preterm miscarriage, fever, hemorrhagic tendency, infection has not been cured, etc.); pregnant women with precious children, informed refusal of interventional prenatal diagnosis; pregnant women who are anxious about interventional prenatal diagnosis; pregnant women who can not book an appointment Pregnant women who are unable to make an appointment for prenatal diagnosis; Pregnant women aged 35-40 years old who refuse invasive prenatal diagnosis; Healthy young pregnant women with a high risk of Down’s syndrome, between 1/270-1/50; Twin pregnancies for whom non-invasive DNA is preferable to be combined with the results of NT screening in early pregnancy. Non-invasive DNA testing is not recommended in the following cases: high risk of Down’s syndrome, greater than 1/50; pregnant women with prenatal ultrasound abnormalities, including early pregnancy with nuchal translucency greater than 3 or 5 mm, early and mid-pregnancy ultrasound findings of any fetal macrostructural anomalies, abnormalities in the amniotic fluid volume, and severe intrauterine growth restriction, etc., pregnancies of three or more fetuses, and pregnant women with a definite chromosomal structural or numerical abnormality in one of the spouses; Pregnant women whose fetus is suspected to have microdeletion syndrome, other chromosomal abnormalities or genetic disorders; Pregnant women who have received allogeneic blood transfusion, transplantation surgery, stem cell therapy, immunotherapy. Invasive fetal chromosome testing Fetal cells are obtained by amniocentesis or chorionic villus aspiration or umbilical cord blood puncture for cell culture and chromosome karyotyping, with amniocentesis being the most widely used. Advantages: (1) It can detect all chromosome number abnormalities and large segments of chromosome structural abnormalities; (2) It is currently the “gold standard” for prenatal diagnosis of fetal chromosomal disorders. Limitations: (1) In general, puncture is relatively safe, but there is still a risk of individual puncture failure, causing miscarriage, infection, amniotic fluid leakage, amniocentesis of the overall fetal loss rate of about 0.5%; (2) individual differences in cell culture can not ensure 100% success; (3) chromosome testing for chromosomal micro-structural changes, monogenic genetic diseases, polygenic genetic diseases, environmental and drug-induced intrauterine development of the fetus. (3) Chromosomal testing cannot completely exclude microchromosomal changes, monogenic genetic diseases, polygenic genetic diseases, environmental and drug-induced intrauterine developmental abnormalities, low chimerism, and maternal contamination. Indications for amniocentesis: maternal age ≥35 years; high risk of fetal chromosomal abnormality on prenatal screening; history of adverse maternal history of fetal chromosomal abnormality; pregnant women suspected of fetal chromosomal disease on prenatal examination; one of the spouses is a carrier of a chromosomal abnormality; pregnant women are likely to be carriers of a certain X-linked genetic disease gene; and those who have a history of adverse maternal history or exposure to specific teratogens. In recent years, it has been advocated that ICSI (intracytoplasmic sperm injection) should also be included in the indication for amniocentesis.