Second‐Trimester Diagnosis of Cri du Chat (5p–) Syndrome Following Sonographic Depiction of an Absent Fetal Nasal Bone

A high association between trisomy 21 and absence of the nasal bone at first-trimester sonography (11-14 weeks' gestation) has been established. 1-3 The presence or absence of the nasal bone was found to be independent of other maternal or fetal variables and thus may be added to other sonographic markers for prenatal detection of trisomy 21. 3 Bromley et al, 4 later Bunduki et al, 5 and others 6 confirmed a mid-second-trimester (15-22 weeks' gestation) association of an absent or hypoplastic nasal bone and trisomy 21. In addition, an absent nasal bone at the 11- to 14-week sonographic scan has been associated with other fetal aneuploidies. 7,8 Cicero et al 7 reported an absent nasal bone in 161 (66.9%) of 242 fetuses with trisomy 21, 48 (57.1%) of 84 fetuses with trisomy 18, 7 (31.8%) of 22 fetuses with trisomy 13, 3 (8.8%) of 34 fetuses with 45,XO, and 4 (8.3%) of 48 fetuses with other aneuploidy defects (XXX, XXY, XYY, and triploidy). The association of an absent or hypoplastic nasal bone and aneuploidies other than trisomy 21 was confirmed by Odibo et al 8 We report a case in which sonographic depiction of an absent nasal bone at 20 weeks' gestation led to amniocentesis and the detection of a fetus with cri du chat (5p-) syndrome.