Fetal nasal bone length at 19-26 weeks' gestation in Vietnam

Aim: The purpose of this study was to establish the normal range of fetal nasal bone length (NBL) at the second trimester of gestation in Vietnamese pregnancies. Methods: A prospective cross-sectional study was carried out. A total of 2432 singleton pregnancies were evaluated for fetal NBL at 19-26 weeks 6 days between 1 January 2013 and 31 December 2014. Three measurements of NBL were taken and the largest value was chosen. Fetal anomalies and neonatal abnormalities were excluded. Results: Mean fetal NBL was 6.75 +/- 0.82 mm and mean gestational age was 22.2 +/- 1.4 weeks. Median NBL increased linearly with advancing gestational age: NBL (mm) = 0.26 x gestational age (weeks) + 1.03 (R2 = 0.20; P < 0.000). The fifth percentile of fetal NBL ranged from 4.6 to 6.3 mm, corresponding with gestational age 19-26 weeks. Conclusion: The normal range ofNBLwas established at second trimester inVietnamese pregnancies. NBL at the fifth percentile for gestational age was different from that of other Asian ethnicities. It is necessary to define short NBL or hypoplasia of NBL with regard to ethnicity.