Fetal nasal bone length in chromosomally normal and abnormal fetuses at 11-14 weeks of gestation.

OBJECTIVE

To determine the value of measuring fetal nasal bone length at 11-14 weeks of gestation in screening for chromosomal defects.

METHODS

The fetal profile was examined and the nasal bone length was measured in 1092 fetuses immediately before chorionic villous sampling for karyotyping at 11-14 weeks of gestation.

RESULTS

The median gestation was 12 (11-14) weeks. The fetal profile was successfully examined in all cases. The fetal karyotype was normal in 955 pregnancies and abnormal in 137, including 79 cases of trisomy 21. In the chromosomally normal group, the fetal nasal bone length increased significantly with crown-rump length (CRL) from a mean of 1.3 mm at a CRL of 45 mm to 2.1 mm at a CRL of 84 mm. In 54 of the 79 (68.4%) cases of trisomy 21, the nasal bone was absent. In the 25 cases with present nasal bone, the nasal bone length for the CRL was not significantly different from normal. Similarly, there were no significant differences from normal in the nasal bone length of fetuses with other chromosomal defects.

CONCLUSIONS

At 11-14 weeks of gestation, the nasal bone length of chromosomally abnormal fetuses is not significantly different from normal.