It is necessary to test for a critical risk of trisomy 21. Critical risk of trisomy 21 is an abnormal test result, and its level of risk is between high risk and low risk. Trisomy 21 is the cause of Down’s syndrome, and some of the affected children will be miscarried during pregnancy, and those who survive will be born with growth retardation, mental retardation, deformities and other pathologies, so pregnant women need to find out if they are at risk of trisomy 21 during pregnancy. A further test for trisomy 21 is non-invasive DNA, which determines whether there is a chromosomal abnormality by taking the serum of the pregnant woman and evaluating the fetus in a comprehensive manner based on gestational week, weight, and age. Amniocentesis is also needed to further confirm the diagnosis. Pregnant women should pay attention to the prenatal examination during pregnancy, actively listen to the advice of professional doctors to do a comprehensive nursing care, pay attention to rest, at the same time should relax, avoid tension, anxiety, any discomfort should be timely to the hospital, the doctor to clarify the diagnosis, and cooperate with the doctor to deal with the symptoms.