First-trimester fetal nasal bone length in an ethnic Chinese population.

OBJECTIVES

To determine reference ranges of fetal nasal bone length (NBL) in a Chinese population and to assess the value of NBL measurement in screening for chromosomal defects in the first trimester.

METHODS

In this prospective study the fetal profile was examined and the fetal NBL and crown-rump length (CRL) were measured in Chinese women presenting with singleton pregnancies for first-trimester screening for aneuploidy between January 2004 and June 2007. Screening was performed on the basis of nuchal translucency (NT) measurement and maternal serum free beta-human chorionic gonadotropin and pregnancy-associated plasma protein-A levels.

RESULTS

NBL was measured in 7543 fetuses, of which 7517 were euploid. The best fit equation for median NBL in euploid fetuses in relation to CRL was: NBL (mm) = 0.4593 + (0.0186 x CRL(mm)). The NBL for gestational age (GA, in days) was given by the equation NBL(mm) = 0.2392 + (0.0027 x GA). There was no correlation between log(10)(NBL multiples of the median (MoM)) and log(10)(NT MoM) in unaffected pregnancies (r = - 0.009; P = 0.43). Only two of the 11 cases with trisomy 21 had an NBL outside the 5(th) or 95(th) centiles of the reference range for euploid fetuses.

CONCLUSION

Reference ranges for NBL in a Chinese population suitable for screening for aneuploidy between 11 and 13 + 6 weeks' gestation have been derived. The NBL in Chinese fetuses is similar to that of other ethnic groups. However, unlike the determination of presence vs. absence of the nasal bone, NBL measurement is unlikely to further improve screening for aneuploidy.