A Thai Reference for Normal Fetal Nasal Bone Length at 11–13(+6) Weeks Gestation

Aim: The purpose of this study was to establish a Thai reference for normal fetal nasal bone length (NBL) at 11–13 +6 weeks gestation. Methods: The fetal nasal bone was measured by sonography in pregnant women at 11–13 +6 weeks gestation. All neonates who showed normal karyotypes were examined after delivery to confirm the absence of congenital abnormalities. Results: A total of 255 pregnant women were recruited. Forty-seven pregnant women were excluded from the analysis because of technically unsatisfactory examination or absent nasal bone and chromosomal abnormalities. The mean ± SD of NBL was 1.79 ± 0.33 mm and increased significantly with crown–rump length (CRL) and gestational age (p < 0.001). The best-fit equation for NBL in euploid fetuses in relation to CRL was: NBL (mm) = (0.030 × CRL (mm)) – 0.016. Conclusion: NBL in Thai fetuses at 11–13 +6 weeks was found to be on average shorter than that in Caucasian, African-American and Chinese populations, but similar to those reported in Korean and Latin-American populations.