Normal fetal nasal bone length at 14 to 28 weeks of gestation

The fetal nasal bone length (FNBL) is a recent sonographic marker included in second trimester genetic sonography which varies with race and ethnicity. The importance of measuring FNBL is in the prenatal diagnosis of Down's syndrome (DS), the most common chromosomal abnormality. Nasal bone hypoplasia or absence is one of the frequent features of DS. Different studies conducted in different parts of the world have established FNBL in different races. But, reference values for normal fetal nasal bone length are yet to be established for Nepalese population. So, the aim of this study was to determine normal FNBL in second trimester. Objective was to create normal reference values for fetal nasal bone in Nepalese population. A cross sectional study was carried out on 150 second trimester pregnancy cases referred for antenatal ultrasound to Department of Radiology at Nepal Medical College and Teaching Hospital between May 2014 and July 2014. Cases included all the clinically normal second trimester pregnancy in which fetal nasal bone could be visualized in midsagittal plane. Table demonstrating normal FNBL corresponding to weeks of gestation was generated using IBM SPSS Statistics Version 20. There was linear increase in mean FNBL with gestational age. Minimum mean FNBL was 2.93 mm at 14 weeks and maximum was 7.89 mm at 27 weeks. Age of patients ranged from 17 to 35 years. Normal FNBL values in Nepalese population corroborates with those published in Western literature but with variation. Hence, reference values for local population become more relevant for antenatal ultrasound practices in Nepal.