The incidence of birth defects in China is as high as 5.6%, with 900,000 new cases of defects each year, including about 25,000 cases of “Down’s syndrome” born each year, which brings a huge emotional and economic burden to the patient’s family and society. Down syndrome, also known as trisomy 21 or Down syndrome, is a disease caused by chromosomal abnormalities (an extra chromosome 21). 60% of affected children are spontaneously aborted in early fetal life, and surviving children have significant intellectual backwardness, special facial features and multiple malformations. Often when doing a maternity checkup, many mothers-to-be are apprehensive, fearing that there is something wrong with their baby …… Whenever they see that the test results are normal, a hanging heart will be put back into the stomach. The first thing you need to do is to have a variety of tests to check the development of your baby. It is believed that many moms-to-be are confused about the choice of different tests, such as Down’s syndrome screening, non-invasive prenatal genetic testing and amniocentesis. I. What is Down’s syndrome screening? Down’s syndrome screening is a common test that screens for the possibility of Down’s syndrome in the fetus. The results are not a final diagnosis, but a risk factor, i.e. the likelihood of developing Down’s syndrome. Down’s syndrome screening is a test that measures the concentration of alpha-fetoprotein, chorionic gonadotropin and free estriol in the mother’s serum, combined with clinical information such as the mother’s age, gestational week, weight, whether she smokes, and whether she has insulin-dependent diabetes, and uses risk assessment software to calculate the risk of having a fetus with congenital defects. The best gestational week for Down’s syndrome screening is 15-20 weeks, and it is recommended that pregnant mothers should have their blood drawn on an empty stomach. Advantages: simple, safe, non-invasive, inexpensive, safe and convenient, and widely available to the population. Disadvantages: low detection rate and accuracy (combined early and mid-term screening only detects 60-80% of children with the disease); high false positive rate (many of those with high risk of Down’s syndrome are not diagnosed as high risk); not suitable for twin or multiple pregnancies. If there is a high risk, further testing is necessary to ensure safety. What is non-invasive prenatal genetic testing? In 1997, a university professor and his research team first discovered the presence of free fetal DNA (cffDNA) in the peripheral blood of pregnant women. With the development of high-throughput sequencing technology, free DNA fragments (including fetal free DNA) in maternal peripheral plasma are sequenced and the sequencing results are analyzed for bioinformatics to obtain fetal genetic information to detect the presence of the three major chromosomal disorders 21/18/13. Because of its high accuracy, rapidity and non-invasive advantages, it has been rapidly transformed from research laboratories to clinical applications, thus creating an era of non-invasive prenatal testing. Applicable gestational weeks: 12-26 weeks, the best gestational weeks for testing is 12-22 weeks. The risk of fetal chromosome aneuploidy, i.e. trisomy 21/18/13, can be accurately determined by collecting 5mL of peripheral blood from pregnant women, extracting free DNA and using new generation high-throughput sequencing technology combined with bioinformatics analysis. Advantages: non-invasive (only venous blood is needed), high detection rate (99% of children are detected), and low false positive rate (very few false positives are diagnosed in non-invasive high risk cases). Disadvantages: There are few formal institutions approved by the state for non-invasive DNA monitoring, it is expensive and has some limitations (scope of testing, population, etc.). Non-invasive DNA is suitable for the following groups: 1. all pregnant women who wish to exclude common chromosomal disorders of the fetus 2. pregnant women with high-risk serum screening in early and mid-pregnancy 3. all pregnant women who need fetal chromosome testing but have contraindications to amniocentesis Non-invasive DNA caution groups: 1. pregnant women with high risk of prenatal screening, advanced age ≥ 35 years old at the due date, and pregnant women with other direct prenatal diagnostic pointers 2, Pregnant women with gestational weeks <12 weeks 3, high weight (weight >100 kg) pregnant women 4, pregnant women with IVF 5, pregnant women with twin pregnancies 6, pregnant women with combined malignant tumors 3, what is amniocentesis? Interventional prenatal diagnosis mainly includes chorionic villus sampling, amniocentesis and cord blood sampling. Amniocentesis is the most widely used in clinical practice. It is usually performed in the middle of pregnancy (around 16w), under real-time ultrasound monitoring, with a fine needle through the abdomen, into the amniotic cavity and then extracting the amniotic fluid, which is then cultured and karyotyped. Applicable gestational weeks: The optimal time for testing is 16-20 weeks of gestation. Under the guidance of ultrasound, a thin needle is passed through the belly of the pregnant woman, through the uterine wall, into the amniotic fluid cavity, and the amniotic fluid is extracted for a comprehensive check. Advantages: Highest accuracy, detects not only trisomy 21 but also other serious chromosomal disorders, and basically covers all chromosomal disorders. Amniocentesis is used as a prenatal diagnostic technique and is still recognized as the “gold standard” for prenatal diagnosis of chromosomal disorders. Disadvantages: invasive test, risk of fetal loss (miscarriage, infection); long testing period (test results take about two weeks). The incidence of Down’s syndrome may occur even in pregnant women with no family history or clear history of toxic exposure, and the incidence increases with maternal age, often by chance and at random. The current state of medical care has no effective treatment for chromosomal disorders. The birth of a child with chromosomal disorders is a great burden for the family and society. Therefore, every couple is advised to do prenatal testing carefully to minimize the risk of having a child with Down syndrome and related chromosomal disorders. Although the choice is indeed painful, only when we have more information will we be more confident in our choice and make a better prediction of the outcome. We wish every pregnant mother a healthy and happy pregnancy.