The critical risk of trisomy 21 cannot be considered serious, it is mainly a question of the degree of risk, representing the possibility of Down’s syndrome is relatively small, but there is a possibility of occurrence, is a situation between high risk and low risk, there is still a certain risk. If Down syndrome occurs, the consequences are more serious, although the critical risk of this situation occurs after birth is trisomy 21 the chances of trisomy 21 is relatively low, but there is still the possibility of occurring, need to weigh the pros and cons of whether to carry out amniocentesis to determine that there is a certain amount of risk to carry out amniocentesis tests. Even if it is a high-risk condition, it is not necessarily a case of Down syndrome, just a higher risk. Critical risk cases can be considered for non-invasive genetic screening to further determine the level of risk.