Trisomy 21 can be prevented during the preparation for pregnancy by doing prenatal and pregnancy checkups, and not being exposed to physical or chemical toxic substances. 1. Prenatal and pregnancy checkups: It is recommended that women should undergo sex hormone 6, ultrasound, secretion, blood and urine routine, immunity antibody and chromosome checkups before pregnancy, and also complete the Down’s syndrome screening test during pregnancy. If the test results show that the fetus is at very high risk of Down’s syndrome, the decision of whether to terminate the pregnancy can be made through negotiation. 2. Do not contact with physical or chemical toxic substances: women should not contact with radiation or toxic substances during pregnancy, and should not blindly take antibiotics or psychotropic drugs, but need to take them under the guidance of a doctor. For unmarried women can reduce the delivery of children with trisomy 21 by the above ways, if necessary, go to a regular hospital, under the guidance of the doctor to prepare for pregnancy physical examination and guidance.