Down screening is recommended during pregnancy to screen for the risk of trisomy 21 and trisomy 18, also known as Down syndrome. When Down’s syndrome results are high or borderline risk, further non-invasive prenatal DNA screening or amniocentesis is required to confirm the diagnosis. If Down’s syndrome is diagnosed, the pregnancy should be terminated promptly, so screening for Down’s syndrome is a very important test in the middle of pregnancy. It is usually done between 15-20+6 weeks. After the pregnancy, pregnant women must remember to have regular maternity checkups to avoid missing the screening time.