Background: Examination of the fetal nasal bone by ultrasound between 11 and 14 weeks gestation has been proposed as an additional tool in the detection of trisomy 21. However, the variability in the identification and the normal length of the fetal nasal bone have not been investigated sufficiently as yet. The aim of this study was to evaluate this parameter and to establish normal ranges for nasal bone length.
Method: Ultrasound examinations were carried out in 122 fetuses at 9, 10, 11, 12 and 20 weeks gestation. On the scans, the fetal profile was examined for the possibility of identification of the nasal bone. Normal nasal bone length reference ranges were generated using prenatal measurements.
Results: The fetal profile was successfully examined in all cases. The nasal bone could first be visualised at 9 weeks gestation. The identification of the fetal nasal bone in all cases was achieved at 12 weeks gestation. The median nasal bone length was 0.29 mm at 9 weeks gestation, 0.96 mm at 10 weeks gestation, 1.73 mm at 11 weeks gestation, 2.25 at 12 weeks gestation, and 6.18 mm at 20 weeks gestation.
Conclusion: The reference ranges for the measurement of the fetal nasal bone length are similar to the findings in the published literature. Only with a knowledge of reference ranges for nasal bone length in normal fetuses can conclusions be drawn about the presence/absence of the bone or the presence of a hypoplastic nasal bone. Further studies are necessary to confirm these results and to obtain larger datasets to assess nasal bone as a quantitative marker.