When is the best time to perform the唐氏筛查 (Down syndrome screening)?

Down syndrome screening is an important prenatal examination used to assess the risk of fetal Down syndrome. The screening is divided into early and mid-term screening, with different optimal timing. Early screening is usually performed between 9 and 13 weeks + 6 days of pregnancy, with the optimal time around 12 weeks. At this stage, the thickness of the fetal nuchal translucency (NT) is measured by ultrasound, and the levels of free β-HCG and pregnancy-associated plasma protein A (PAPP-A) in maternal serum, along with maternal age, are used to calculate the risk. Mid-term screening occurs between 15 and 20 weeks of pregnancy, with the optimal time around 16 to 18 weeks. At this stage, maternal serum alpha-fetoprotein (AFP), free β-HCG, and unconjugated estriol (uE3) levels, along with maternal age and other parameters, are used to assess the risk. Therefore, pregnant women should visit a qualified hospital for blood tests within the above-mentioned timeframes and take the results seriously. If necessary, further diagnostic tests such as amniocentesis or other confirmatory examinations should be considered. Additionally, pregnant women should maintain emotional stability during pregnancy and avoid excessive anxiety, which may negatively affect fetal growth and development.