Foetal Nasal Bone Length Measurement and Evolving Normogram in Southern Indian Population in Normal Pregnancies: A Cross-sectional Study

Abstract

Introduction: Assessment of the foetus to detect aneuploidies between 12 to 24 weeks of gestation is an integral part of the ultrasound scanning. Absence or hypoplastic nasal bone is a very important marker of foetal aneuploidy. Thus, identifying the range of foetal Nasal Bone Length (NBL) in normal gestation is very important to screen for aneuploidies. Aim: This study aimed at ascertaining the reference range of foetal NBL between 11 to 24 weeks of pregnancy. Materials and Methods: A multicentre, cross-sectional study was conducted from 2018 to 2020. After obtaining Ethical approvals from each centre, NBL was measured in 826 patients between 11-24 weeks of pregnancy. Transabdominal scans were performed and the data was used to construct the NBL normogram for this Gestational Age (GA). Linear regression analysis was used to analyse the relationship between NBL and Gestational Age. Scatter plots for NBL as function of GA was constructed. The 5th and 50th percentile values were calculated for each gestational week. Results: With one unit increase in GA (weeks), NBL increased by 0.402 times (r=0.897, p<0.001). Mean NBL was 4.05 mm. The medians NBL for 12-14 weeks were 2.1-2.5 mm, 15-18 weeks was 3.0-4.6 mm, 19-21 weeks was 5.3-5.8 mm, 22-24 weeks was 6.0-6.6 mm. Conclusion: This study highlights the importance of nasal bone evaluation in the second trimester of pregnancy to detect foetuses with Down syndrome. Since NBL increases linearly with GA, it aids detecting the hypoplastic nasal bone at different GA.