Absent fetal nasal bone in the second trimester and risk of abnormal karyotype in a prescreened population of Chinese women

Introduction: The aim of this study was to evaluate the value of absent fetal nasal bone in the prediction of fetal chromosomal abnormalities, according to whether it was associated with other soft markers or structural abnormalities in a prescreened population of Chinese pregnant women.

Material and methods: In this retrospective cohort study, women whose fetuses had absent nasal bone detected during the second trimester ultrasound scan were followed. Fetal karyotyping was performed and pregnancy outcomes were recorded. The association between absent fetal nasal bone with abnormal karyotype was evaluated according to whether soft markers or structural abnormalities were also observed.

Results: Fetal nasal bone was assessed in 56 707 singleton pregnancies. After exclusion of unqualified cases, 71 (71/56 707, 0.13%) fetuses were included in the final analyses, of which 16 (16/71, 22.54%) were detected to have chromosomal abnormalities, including 12 cases of trisomy-21, three of trisomy-18, and one of micro-deletion (in 7q). Among the 42 cases with isolated absence of nasal bone, two had trisomy-21 and one had a micro-deletion. Absence of nasal bone in association with other structural abnormalities had a higher rate of abnormal karyotypes compared with isolated absence of nasal bone [83.33% (10/12) vs. 7.14% (3/42), Fisher's exact test χ² = 25.620, p < 0.001].

Conclusion: Absent fetal nasal bone is a highly specific ultrasonographic soft marker that should be included in the routine second trimester ultrasound scan.