Down’s syndrome, you may feel both familiar and unfamiliar. Women who have had babies know that there is a test that is done during pregnancy called: Down’s syndrome screening. It is said to screen for Down’s syndrome. Some of you may be wondering: how can you look at someone and say they are a Down’s child? The three words “Down’s child” are written on their faces? Well, it’s really written on their faces! How to identify children with Down’s syndrome? Down’s children have typical facial features: small and round head, thick and short neck, wide eye spacing, flat nose, small eye fissure, mouth half open, tongue out. These children are mentally retarded and have an almost identical face, which is called the “international face”. This is a person with Down syndrome. We used to see such silly children, but now they are rare, thanks to the very popular Down’s syndrome screening during pregnancy. Why does Down syndrome occur? Down syndrome, also called trisomy 21, is the most common chromosomal disorder in human newborns, accounting for more than 90% of chromosomal disorders, because the patient has one more chromosome pair 21 than normal, three compared to two for normal people. Every pregnant woman can have a child with Down’s syndrome. The chance of having a child with Down’s syndrome rises with the age of the pregnant woman. Children with Down’s syndrome are severely mentally challenged, unable to take care of themselves, and have complex cardiovascular disease, requiring long-term care by their families, which can cause a great emotional and financial burden to the family. Therefore, almost all developed countries perform Down’s syndrome screening for pregnant women. When should I be screened for Down’s syndrome? There are two periods for Down’s syndrome screening: 11 to 14 weeks of pregnancy, called early screening; and 14 to 21 weeks of pregnancy, called mid-term screening. 1. Early screening: also known as NT test, NT refers to the thickness of the nuchal translucency layer of the fetus. It is an ultrasound screening program during early pregnancy and is the first step to rule out fetal abnormalities. The NT test requires high technical requirements of the ultrasonographer and the configuration of the ultrasound machine, and the examination also depends on the position of the baby, if the baby’s position is not good, the best detection plane cannot be obtained, and the NT measurement will be inaccurate, so the NT test is the main bottleneck of the early tang that cannot be carried out on a large scale. The thicker the NT value, the higher the chance of fetal abnormalities, mainly fetal chromosomal abnormalities. NT thickening can better assess the risk of fetal development of trisomy 21, trisomy 18 and trisomy 13. Fetal NT can screen more than 75% of fetuses with Down’s syndrome and other severe chromosomal abnormalities. Generally speaking, NT thickness >3mm indicates the possibility of adverse fetal outcome and needs to be recorded in a focused manner to facilitate later Down’s syndrome screening and 4D ultrasound screening, prompting the doctor to focus on it. 2. Mid-term screening: It is the familiar Down’s syndrome screening. This is done by testing the blood of the pregnant woman and combining it with other clinical information to determine whether she is at high risk or low risk. If the test is high risk, further testing is required to determine if the defect is really present through amniocentesis or non-invasive DNA testing. Amniocentesis carries a risk of rupture of the amniotic membrane and a 1 percent chance of miscarriage. Compared to traditional Down’s syndrome screening, non-invasive DNA testing is similar to a high-powered “microscope”, which only requires 5 ml of venous blood from a pregnant woman and directly detects the fetal free DNA in the plasma. The test can detect whether the baby has Down’s syndrome with an accuracy rate of 99%. It is harmless to both mother and baby. In general, the screening is done for pregnant women under 35 years old, and for those over 35 years old, twins, or those who are financially able to do so, if the non-invasive DNA finds abnormalities, a final diagnosis will be made by chorionic villus biopsy or amniocentesis to decide whether to terminate the pregnancy. There is no effective prevention or treatment. In December 2011, the United Nations General Assembly designated March 21 as “World Down Syndrome Day”. This day was chosen because of the uniqueness of Down syndrome – the trisomy of the 21st chromosome pair. Since 2012, the General Assembly has invited all Member States and relevant organizations of the United Nations system to observe World Down Syndrome Day in an appropriate manner in order to raise public awareness of Down syndrome. Currently, there is no effective prevention or treatment for the disease, and early detection is possible only through prenatal screening.