First-trimester examination of fetal nasal bone in the Chinese population.

Objectives: Absence of the nasal bone in fetuses with trisomy 21 is a potential ultrasound marker for Down syndrome from the first trimester onwards. Racial differences in fetal nasal bone length have been reported. There was no reference range for the first-trimester fetal nasal bone length (NBL) in the Chinese population.

Methods: From January 2002 to February 2005, we investigated the reference range of NBL in 2169 singleton fetuses whose parents were Chinese with normal pregnancy outcome. Ultrasound measurements of NBL were performed on a midsagittal plane at 12-14 weeks' gestation.

Results: The nasal bone length measurement showed a significant increase with gestational age (GA) (p < 0.05). A linear relationship between nasal bone length and gestational age (NBL = -3.3462 x GA + 0.627, R(2) = 0.30, p < 0.001) as well as a linear relationship between nasal bone length and crown-rump length (CRL) (NBL = 0.3741 x CRL + 0.284, R(2) = 0.30, P < 0.001) was established.

Conclusion: The measurement of nasal bone length was feasible in the first trimester. The reference range of NBL in normal Chinese fetuses in the first-trimester of pregnancy was established. This formed a basis for further study on the use of fetal nasal bone measurement in the screening for aneuploidy in the Chinese population.