Down screening is based on ultrasound, maternal blood and other tests, combined with maternal age, weight, gestational week and other aspects to determine the risk factor of fetal congenital stupidity and neural tube defects, the specific screening time varies according to the screening program, there are usually the following: 1, early pregnancy duplex screening: blood tests are performed at 7-13 weeks of pregnancy, through the detection of serum pregnancy-related protein-A and human chorionic gonadotropin ( The best time for the test is 11-14 weeks of pregnancy, and the thickness of the nuchal translucency layer is measured by ultrasound to assess whether the fetus is at risk of Down’s syndrome; 3. Duplex screening serum alpha-fetoprotein (AFP) and HCG or free β-HCG as indicators, and triple screening refers to serum AFP plus HCG (or free β-HCG) plus unconjugated estriol as indicators, combined with maternal age and other parameters, to calculate the risk of fetal disease. The results of Down screening are usually available in about 1 week, and if the result is low risk, it is considered normal. If the risk is judged to be high, an invasive test is needed to confirm the diagnosis by obtaining cell samples from the placenta through chorionic villus sampling, or amniocentesis to obtain cells shed from the fetus in the amniotic fluid and test the cells for chromosomes to confirm whether the fetus is a Down’s child.