The currently accepted methods of Down’s syndrome screening are divided into traditional Down’s syndrome screening and non-invasive prenatal genetic testing, with different screening times. The traditional Down’s syndrome screening is divided into early Down’s syndrome screening and mid-term Down’s syndrome screening, and the early Down’s syndrome screening is at (9-13) weeks + 6 days, and the mid-term Down’s syndrome screening is at (15-20) weeks + 6 days, provided that the week of gestation is checked accurately. 1.Traditional Down screening 1.Early pregnancy combined screening: including ultrasound measurement of fetal nuchal translucency layer thickness and maternal serological examination, serological testing indicators include pregnancy-related plasma protein-A and free β-human chorionic gonadotropin, early pregnancy serological screening blood collection time is (9-13) weeks + 6 days; 2.Mid pregnancy screening: serological markers combined screening, including methemoglobin, human 2. Mid-gestation screening is a combination of serological markers, including alpha-fetoprotein, human chorionic gonadotropin or free beta-human chorionic gonadotropin, free estriol, and quadruple screening with an increase in inhibin A. The gestational week is usually (15-20) weeks + 6 days. Non-invasive prenatal genetic testing should be performed after 12 weeks of pregnancy, and the appropriate gestational week for testing is 12-22 weeks of pregnancy. Although the accuracy of non-invasive prenatal genetic testing is high, it is not recommended under the risk of other chromosomal or genetic diseases of the fetus.