The term prenatal screening is usually used to refer to a blood test that detects pregnant women at high risk of carrying a fetus with certain congenital defects through the detection of certain substances (called markers) in the mother’s serum. Further tests (such as amniotic fluid extraction, diagnostic ultrasound, etc.), also known as prenatal diagnosis, are performed on high-risk pregnant women. Severely defective fetuses are found to require termination of pregnancy to minimize the birth of abnormal fetuses. Prenatal screening methods are convenient and non-invasive. The screening targets are general pregnant women less than 35 years old, and older pregnant women older than 35 years old are recommended to do prenatal diagnosis directly because the incidence of chromosomal diseases is significantly higher than that of general pregnant women. The prenatal screening carried out by Lin Yi of the Department of Obstetrics and Gynecology at Ningbo Women’s and Children’s Hospital is still relatively limited in terms of the diseases it can screen for, mainly screening for trisomy 21, trisomy 18 and neural tube abnormality, three of the more common congenital abnormalities in fetuses, but during the screening process, some other aspects of the disease, such as internal organ malformations, serious heart disease, etc. can also be detected. Prenatal screening is usually performed between 15-19 weeks. For pregnant women with high risk of prenatal screening, amniocentesis or cord blood testing is recommended.