Many people do not know what trisomy 21 is. But when it comes to children with Down’s syndrome or congenital stupidity, everyone understands that trisomy 21 is a genetic defect disease, the intelligence of children with trisomy 21 is lower than normal children, usually their IQ is only about half that of normal children, and children with Down’s syndrome also have delayed development and muscle tension, so their learning and walking are worse than normal children. How trisomy 21 is triggered. Most of the trisomy 21 children are newborns: this has nothing to do with the chromosomal nuclei of the parents, but mainly with the process of embryonic development, which has a lot to do with the quality of women’s eggs, the older the women are, the older the eggs are, the less likely they are to separate. 2, there are also some reasons related to genetics: if the couple has given birth to a child with Down’s syndrome, then it is best to do a chromosomal examination, so that the genetic factors can be discharged, so that the next pregnancy to do a certain reference, in addition to less exposure to radiation during pregnancy. 3, scientific methods to avoid deformed children: In addition, there are now many medical methods for Down’s syndrome detection during pregnancy, combined with maternal age, gestational weeks, if the abnormal calculation of Down’s syndrome fetus, the risk of pregnancy, should also be performed amniocentesis. So it requires that women must do a good job of pregnancy tests during pregnancy. 4, precautions: through the above introduction, I think we must have a more comprehensive understanding of trisomy 21, trisomy 21 in our lives is more common in a defect-based disease, so the pregnancy test becomes particularly important.