trisomy 21
noun [ U ] medical specialized (also Trisomy 21) /ˌtrɪ.sə.mi twen.tiˈwʌn/ /ˌtraɪ.soʊ.mi twen.t̬iˈwʌn/
（最常见的唐氏综合征、因多出一条21号染色体而引起的）21三体
the most common form of Down's syndrome (= a genetic condition associated with learning difficulties in which a person is born with an extra chromosome) that is caused by there being an extra copy of the chromosome number 21 in the body's cells
Their first child has trisomy 21 and they want to know the risk of having another child with Down's syndrome. 他们的第一个孩子有21三体，因此他们想知道第二个孩子得唐氏综合征的风险有多少。
Pregnant women can screen for Trisomy 21, a chromosomal abnormality, through a blood sample. 孕妇可通过血液检查来筛查胎儿是否患有21三体，一种染色体异常疾病。
- More examples
- In the past year I have identified two cases of trisomy 21 in our screening district.
- The proportion of cases of trisomy 21 diagnosed cytogenetically before birth rose.
- This Trisomy 21 diagnosis – Down syndrome, in lay terms – was followed not by smiles and "Congratulations! You just had a baby" joy, but by downcast eyes and pity.