High risk of noninvasive trisomy 21 has the potential for amniocentesis reversal. Non-invasive DNA is to extract peripheral blood of pregnant women to check the fetal risk rate of trisomy 21, trisomy 18, trisomy 13, non-invasive DNA has a high detection rate, low false positive rate, but checking out the high risk of trisomy 21 is not necessarily diagnosed, but also need to carry out amniocentesis. So non-invasive DNA high risk of trisomy 21 still has the possibility of amniocentesis flopping. Amniocentesis is a chromosomal genetic disease diagnosis by drawing amniotic fluid and doing fetal karyotyping. Non-invasive DNA is sometimes affected by maternal or weight factors, resulting in errors in the results, if the fetus is determined not to have trisomy 21 by amniocentesis, flopping is also possible. Pregnant women at high risk for non-invasive trisomy 21 are advised to actively cooperate with the doctor’s recommended diagnosis and treatment.