Absent nasal bone in the prenatal detection of fetuses with trisomy 21 in a high-risk population.

Abstract

To estimate the usefulness of absent nasal bone by ultrasound in the prenatal detection of second-trimester fetuses with trisomy 21.
This was a matched case-control study of sonograms from January 1, 1997 to April 30, 2002. Genetic sonograms and facial profile pictures of all fetuses that were subsequently proven to have trisomy 21 were reviewed (study group). A control group was identified during the same study period by using a 4-to-1 ratio matching for gestational age at the time of the ultrasound examination. The sensitivity and specificity of absent fetal nasal bone for trisomy 21 were determined, and overlap with other ultrasound aneuploidy markers was assessed.
Forty fetuses were identified with trisomy 21; in 29 (72.5%) a facial profile had been obtained. Of the 160 controls, 102 (64%) had facial profiles documented. Of the 29 fetuses with trisomy 21 with facial profile available, 12 had absent nasal bone (sensitivity 41%). None of the 102 control fetuses with facial profiles available had absent nasal bone (specificity 100%). The sensitivity of genetic ultrasound was increased from 83% (24 of 29) to 90% (26 of 29) by adding absent nasal bone to the other ultrasound aneuploidy markers.
In the second trimester of pregnancy, absent nasal bone has a sensitivity of 41% and a specificity of 100% in detecting fetal trisomy 21. Absent fetal nasal bone may be added to the list of ultrasound aneuploidy markers evaluated during a genetic sonogram.