Ethnic variation of fetal nasal bone length between 11-14 weeks' gestation

Article Outline

• Objective
• Study design
• Results
• Conclusion
• Copyright

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Objective 

To assess the potential effect of ethnicity on the development of the fetal nasal bone (NB).

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Study design 

Between October 2003 and June 2004 we measured the FNBL in a pilot cohort of 188 patients undergoing first trimester ultrasound at 11-14 weeks' gestation. Our study population consisted of 4 ethnic groups: Asian (G1: 24 patients from China, India, and Pakistan), Black (G2: 25 patients of African-American, Dominican, and Caribbean ancestry), White (G3: 49 patients), and Hispanic (G4: 86 patients). Patients were informed that the clinical significance of this measurement remains investigational and the recommendation for invasive testing was based upon standard indications (e.g., maternal age, nuchal translucency (NT) measurement, and serum markers) only. Prior approval of the study by the IRB was obtained. Measurements of the NB length were performed after obtaining the midsagittal view of the fetus with the ultrasound beam parallel to the NB. Comparison between the groups was performed by using one-way ANOVA and chi-square test.

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Results 

188 patients were included in this pilot study as noted above. Four patients were excluded from the study since their ancestry was mixed. The FNBL correlated with the CRL (0.45, P < .01). The NB was absent in one fetus (normal outcome), and could not be technically obtained in 9 fetuses (4.8%). Comparing between the 4 groups (G1, G2, G3, and G4) there were no statistical differences in CRL (62+8.8 mm; 58.5+15.6 mm; 60.8+14.7 mm; 60.1+14 mm, respectively) or the NT (1.46+0.4 mm; 1.25+0.4 mm; 1.33+0.5 mm; 1.35+1 mm, respectively). However, the FNBL was statistically different (2.2+0.4 mm; 2.5+0.6 mm; 2.9+0.7 mm; 2.5+0.6 mm, respectively, P < .001) comparing between these groups (G1, G2, G3, and G4).

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Conclusion 

Absence of the nasal bone and nasal bone hypoplasia are recognized to be potential sonographic markers for trisomy 21 in both the first and second trimesters. The FNBL should be adjusted for ethnicity when introducing this tool for first trimester screening purposes.