| Q90 | Down syndrome |
| Q90.0 | Trisomy 21, nonmosaicism (meiotic nondisjunction) |
| Q90.1 | Trisomy 21, mosaicism (mitotic nondisjunction) |
| Q90.2 | Trisomy 21, translocation |
| Q90.9 | Down syndrome, unspecified |
| Q91 | Trisomy 18 and Trisomy 13 |
| Q91.0 | Trisomy 18, nonmosaicism (meiotic nondisjunction) |
| Q91.1 | Trisomy 18, mosaicism (mitotic nondisjunction) |
| Q91.2 | Trisomy 18, translocation |
| Q91.3 | Trisomy 18, unspecified |
| Q91.4 | Trisomy 13, nonmosaicism (meiotic nondisjunction) |
| Q91.5 | Trisomy 13, mosaicism (mitotic nondisjunction) |
| Q91.6 | Trisomy 13, translocation |
| Q91.7 | Trisomy 13, unspecified |