Down’s syndrome screening is to screen the fetus for chromosomal disorders, early pregnancy Down’s syndrome screening serologic indicators for maternal PAPPA and HCG levels, combined with fetal gestational weeks and NT data calculated by the integrated risk value. At 11 weeks plus 6 days to 13 weeks of a woman’s pregnancy, ultrasound is used to check the thickness of the fetal nuchal translucency so as to determine whether the fetus has a chromosomal abnormality; a normal fetus should be less than 2.5 millimeters, and if it exceeds that, it needs to undergo a mid-term Down’s screening or amniocentesis to confirm the diagnosis. The risk of Down’s syndrome is determined by taking the pregnant woman’s venous blood and checking her blood for alpha-fetoprotein, human chorionic gonadotropin, and estriol. If the risk is high, amniocentesis or chorionic villus puncture is needed to confirm the diagnosis. Down’s syndrome screening is a key prenatal screening test, and effective testing can prevent the birth of Down’s syndrome babies.