Mid-Second Trimester Measurement of Nasal Bone Length in North Indian Population

INTRODUCTION

Nasal bone is an indispensible parameter in the second-trimester ultrasound. Nasal bone measurements vary according to race and ethnicity. Most of the criteria and normogram have been established according to race and origin. Till date, there have been no established criteria for nasal bone measurement in the second trimester in North Indian population which is 199 million.^[1]

The absence or hypoplasia of the fetal nasal bone in children with Down syndrome can be detected by the first- and second-trimester sonography.^[2] A depressed nasal bone and short neck with increased uncial thickness are some common features found at the time of ultrasonography and after delivery in neonates.^[3] Healthy fetal nasal bone length (NBL) values have been established in Caucasian, African, American, and South American populations.^[4] Thus, ethnicity may impact fetal NBL. This study sought to determine a reference range for the second-trimester NBL in fetuses in a North Indian population and compare our findings with NBL findings reported in other populations.

MATERIALS AND METHODS

This is a retrospective study conducted on North Indian pregnant women ranging from 14 to 22 weeks of gestation conducted in Era’s Lucknow Medical College and Hospital in Lucknow from 2014 to 2018. In our study, 2060 North Indian women who underwent ultrasonography were recruited. Informed consent was taken and ethics committee approval was obtained. All patients were registered under PC-PNDT Act of India, 1994. The criteria used for exclusion were abnormal karyotypes, fetal anomalies, fetal death in utero, absent nasal bone, and structural anomalies.

The measurement of the fetal NBL was performed by the double operator method with a mid-sagittal view of the fetal head to identify the nasal bone, lips, maxilla, and mandible with an angle from 45° to 135 degrees to the ultrasound beam, following the Sonek et al. method [Figure 1].^[5] Three images were obtained for each patient, and one measurement per image was taken for each patient. Fetal growth parameters (biparietal diameter, head circumference, abdominal circumference, and femoral length) were assessed for each fetus. In each case, fetal measurements were taken by ultrasound (Voluson P9, GE Health Care, Vienna, Austria). After data collection, statistical analysis was performed. The 5^th and 50^th percentile values of 2060 recruited pregnant women were calculated for the reference gestational weeks.

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Figure 1

Sagittal gray scale ultrasound image of an intrauterine fetus of gestational age 16 weeks, 3 days showing the measurement method of fetal nasal bone (arrow) as described by Sonek et al.^[5]

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RESULTS

The rate of growth of the fetal nasal bone during different weeks of gestation is described by an equation where NBL = 0.365×gestational age (GA)+ 2.5885, with a fit estimate of R² = 0.97, P < 0.001. The median NBL increased with GA from 2.9 mm at 14 weeks to 5.8 mm at 22 weeks in a linear relationship. The mean NBL was 4.63 mm, and the overall standard deviation was 0.925. The 5^th and 50^th percentile NBLs for each GA are shown in Table 1. The 5^th percentile signified the nasal hypoplasia/aplasia. The NBLs were closer to those of the South Indian populations, but our findings were different from those found in the Chinese and Japanese populations, as shown in Table 2.^[6-8] The difference in the mean was found to be statistically significant between North Indian population and Chinese population (P < 0.001). Mean and standard deviation values were unavailable for Japanese populations. The 50^th percentile of NBL in our North Indian population was also similar to that of South Indian populations, as shown in Table 3. The linear model was preferred for finding the relationship between mean NBL and GA as shown in the scatter plot of Figure 2.

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Figure 2

Scatter plot showing the relationship between mean fetal nasal bone length and gestational age of the fetus (14–22 weeks) in our study.

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DISCUSSION

Association of hypoplastic or absent nasal bone with various congenital anomalies makes it an indispensable parameter of second-trimester ultrasound. Nasal bone measurements vary according to race and ethnicity.

In contrast to Narayani and Radhakrishnan, the NBL at 16 and 22 weeks in our study was 3.5 mm and 5.8 mm, respectively, which was on the higher side as compared to them.

In the previous studies, the isolated finding of absent/hypoplastic nasal bone was associated with chromosomal disease in 10%–12% of cases. Ultrasound anomalies were noted in 41.4% of absent/hypoplastic nasal bone cases, and abnormal chromosomes were noted in 28.5% of cases involving high-risk biochemical studies.^[3] These detection rates were likely similar to those of the second-trimester maternal serum biochemical screening tests.^[8]

CONCLUSIONS

NBL is an objective measurement in clinical practice. The NBL in North Indian fetuses at 14 to 26 weeks of GA has a linear relationship to the week of gestation. Our study confirmed significant differences in the 50^th percentile NBLs between Chinese and Japanese populations and our north Indian population, and we found a close relationship with subtle differences between North and South Indian populations.