Absence of nasal bone in fetuses with trisomy 21 at second trimester of pregnancy

Objectives: To investigate the value of second-trimester ultrasound assessment of fetal nasal bone (NB) in predicting trisomy 21. Methods: A retrospective analysis was performed on the test results of pregnant women who received amniocentesis besides their anomaly scan due to various reasons at the Prenatal Diagnosis Center of Fudan University Obstetrics & Gynecology Hospital from January 2012 to January 2016. The ultrasound screening and chromosome screening results of fetuses with absent NBs were recorded. Results: The rate of NB absence in the fetus group with trisomy 21 was 8.43%, significantly higher than the rate of the euploid fetus group, 0.36% (P < 0.05). The rate of trisomy 21 in the fetus group with non-isolated NB absence was 87.5% (14/16), far higher than the rate of the group with isolated NB absence, 4.5% (1/22) (P < 0.05). Conclusions: Second-trimester ultrasound screening for absence of the fetal NB, especially for non-isolated NB absence is useful in detecting fetuses with trisomy 21.