The nasal bone was absent in 43 of 59 (73%) trisomy 21 fetuses and in three of 603 (0.5%) fetuses with normal karyotype.

• 在59名第21对染色体三体的胎儿中有43名(73%25)出现了鼻骨缺失，在正常染色体组合的603名胎儿中有3名(0.；5%25)出现鼻骨缺失。