# A Nomogram of Fetal Nasal Bone Length at 16-24 Weeks of Gestation in North Indian Pregnant Women: A Prospective Study

## TL;DR

This study creates a reference chart for fetal nasal bone length in North Indian pregnancies to improve prenatal screening accuracy.

## Contribution

A gestational age-specific nomogram for fetal nasal bone length in North Indian populations is developed.

## Key findings

- Fetal nasal bone length increases significantly with gestational age in North Indian pregnancies.
- Strong correlations exist between nasal bone length and other fetal biometric parameters like BPD and HC.
- Ethnic-specific reference values are recommended to improve prenatal screening accuracy.

## Abstract

Introduction

Fetal nasal bone length (NBL) is a crucial sonographic marker in prenatal screening for chromosomal abnormalities, particularly trisomy 21. However, its diagnostic accuracy is influenced by ethnic variations, and normative data for North Indian populations remain scarce.

Objective

This study aimed to establish a gestational age-specific nomogram for fetal NBL between 16+1 and 24 weeks of gestation in North Indian pregnant females, and to evaluate its correlation with standard fetal biometric parameters.

Methods

A prospective observational study was conducted on 438 structurally and chromosomally normal North Indian pregnant females. Fetal NBL was measured using mid-sagittal ultrasound imaging, and participants were stratified into two gestational age groups, A and B. Group A includes 16-20 weeks of gestational age, and Group B includes more than 20 to 24 weeks of gestational age. Percentile distributions were calculated, and correlations between fetal NBL and other biometric parameters (biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL)) were assessed.

Results

Mean fetal NBL increased significantly with gestational age (4.56 mm in Group A vs. 5.74 mm in Group B; p < 0.001). Strong positive correlations were found between fetal NBL and BPD (r = 0.926), HC (r = 0.903), and AC (r = 0.874), while a moderate correlation was noted with FL (r = 0.402). The fifth-percentile thresholds for fetal NBL were 3.70 mm (Group A) and 5.10 mm (Group B).

Conclusion

This study provides a population-specific nomogram for fetal NBL in North Indian pregnancies during the second trimester. The findings underscore the importance of using ethnicity-specific reference values to improve the accuracy of prenatal aneuploidy screening and to reduce false-positive diagnoses.