Prenatal screening methods and programs vary depending on the gestational week of the pregnant woman. The main clinical prenatal screening programs are as follows: 1. NT screening: screening program for women in early pregnancy; 2. Early pregnancy Down syndrome screening, which is done by ultrasound means to measure the thickness of the zona pellucida behind the baby’s neck and then combined with blood test results to screen for Down syndrome, i.e. screening for Down’s syndrome. It is usually done at 12 to 14 weeks.3 The intermediate screening period is from 15 weeks to 20+6 weeks, and the peripheral blood of the pregnant woman is taken to test for pregnancy-related plasma protein A, free beta chorionic gonadotropin, methemoglobin and free estriol. Based on the laboratory test results, the couple’s medical history, physical examination and ultrasound examination are combined to perform risk assessment and distinguish pregnant women into low-risk and high-risk groups. Pregnant women who are at high risk and whose due ages are 35 years or older and other reasons require direct prenatal diagnosis are referred to prenatal diagnostic institutions for amniotic fluid diagnostic testing, and pregnant women whose prenatal screening results are critical or who miss prenatal screening can undergo noninvasive DNA diagnosis .