If a critical risk of trisomy 18 is found during the Down’s syndrome screening, the condition is not serious at this time and should not be overly stressed. Further tests should be done after this occurs, and non-invasive DNA tests can be done to determine the specific condition of the baby. If the baby is still at critical risk during the non-invasive DNA test, amniocentesis is needed because both Down’s syndrome screening and non-invasive DNA tests are performed by extracting the pregnant woman’s serum for comprehensive analysis, and cannot directly detect the specific condition of the fetus. The amniocentesis is a direct analysis and judgment of the baby’s amniotic fluid, which is the final result and the gold standard.