Evaluating the efficiency of using second-trimester nasal bone hypoplasia as a single or a combined marker for fetal aneuploidy.

OBJECTIVE Although second-trimester nasal bone (NB) hypoplasia has been associated with fetal aneuploidy, its role as a single marker is still uncertain. Our objective was to evaluate the efficiency of NB hypoplasia as an independent marker for fetal aneuploidy. METHODS This was a prospective cohort study of women undergoing an anatomic survey between 16 and 22 weeks' gestation. The fetal NB and other markers of fetal aneuploidy, including nuchal fold, femur and humeral lengths, choroid plexus cysts, major fetal anomalies, echogenic bowel, pyelectasis, and hypoplastic fifth digits, were evaluated. Nasal bone hypoplasia was defined either as an absent NB or by a ratio of the biparietal diameter to NB. Fetuses or infants with fetal aneuploidy were compared with those without for the presence of NB hypoplasia either as a single marker or in the presence of other markers for aneuploidy. RESULTS Of 2885 women evaluated, NB measurements were obtained in 2465 (85%). There were 35 (1.4%) cases with fetal aneuploidy. The sensitivity and specificity of a single NB in detecting Down syndrome varied from 23% to 64% and 57% to 99%, respectively, depending on the definition of NB hypoplasia used. There was an improvement in the efficiency of using the NB when combined with other markers, with sensitivity and specificity increasing from 59% to 82% and 74% to 87%, respectively. CONCLUSIONS Nasal bone hypoplasia is a marker for fetal aneuploidy. The combination of the NB with other makers was associated with an improvement in detection of fetal aneuploidy.