Pregnant women can have Down’s syndrome screening at 20 weeks of pregnancy. Generally, Down’s syndrome screening is done at 15-20 weeks, and the best time is 16-18 weeks, and the results of Down’s syndrome screening are more accurate in this time period. The Down’s syndrome screening is a test to determine the concentration of alpha-fetoprotein, human chorionic gonadotropin and free estriol in the mother’s serum, and to determine the risk of congenital stupidity and neural tube defects in conjunction with the mother’s age, weight and gestational week. You do not need to have an empty stomach for Down’s syndrome screening, and you can drink water. However, you need to eat a light diet and avoid oily and spicy food. Before the test, you need to provide detailed personal information about the pregnant woman, including the year of birth, last menstruation, weight, whether you have insulin-dependent diabetes, twin pregnancies, whether you smoke, and whether you have a history of abnormal pregnancies. During the examination, the doctor gives a report that shows a high-risk condition and the pregnant woman also needs a non-invasive DNA test or an amniocentesis test. If you are already over 20 weeks, it is not recommended to do Down’s screening. Pregnant women can do the non-invasive DNA test within 24 weeks of pregnancy, which is more accurate than the Down’s screening.