Ultrasound evaluation of the length of the fetal nasal bones throughout gestation.

Subtle facial abnormalities, including smallness of the nose, are common findings in trisomy 21 and numerous other genetic conditions. The aim of this study was to construct a normal range for the length of the fetal nasal bones with gestation in a Caucasian population. Ultrasound measurements were performed on a strictly mid-sagittal profile in 376 normal singleton fetuses at 14-34 (mean 24) weeks' gestation. It was found that the length of the nasal bones increased from 4 mm at 14 weeks to 12 mm at 35 weeks' gestation, and that there was a linear relationship between the length of these bones and biparietal diameter and femur length. We conclude that the length of nasal bones can easily be measured in fetuses at 14-34 weeks' gestation and that such measurements might prove useful in the evaluation of pregnancies at high risk for associated fetal abnormalities.