Fetal Nasal Bone Length in the Period of 11 and 15 Weeks of Pregnancy in the Filipino Population

Leodoro J. Labrague, Lynette C. Tan

  Open Access OPEN ACCESS  Peer Reviewed PEER-REVIEWED

Fetal Nasal Bone Length in the Period of 11 and 15 Weeks of Pregnancy in the Filipino Population

Leodoro J. Labrague1,, Lynette C. Tan2

1Samar State University, Philippines

2University of Santo Tomas, Manila, Philippines

Abstract

In the recent years, sonographic images of fetal nose have gained popularity in detecting trisomy 21 and other aneuploidies. Reference values for nasal bone length have been reported in different countries and ethnic populations. However, there was no reference range for the fetal nasal bone length (NBL) in the Filipino population. This prospective, cross-sectional study was conducted to establish reference values for the nasal bone length (NBL) at 11 – 15 weeks of gestation in the Filipino population. Ultrasonographic visualization of 74 fetuses at 11th to 15th week gestation was carried out during the months of August 2010 to January 2011. Fetal nasal bone was measured through sagittal section of the fetal profile. Fetal nasal bone length measurement was successfully performed in all 74 cases. The mean nasal bone lengths were 1.97 mm, 2.37 mm, 2.90 mm, 3.49 mm, and 4.05 mm between 11th, 12th, 13th, 14th, and 15th gestational weeks respectively. Nasal bone length increased linearly with advancing gestational age (GA) and crown rump length (CRL). Despite of the limitations posed by this investigation, reference values for the nasal bone length (NBL) at 11 – 15 weeks of gestation in the Filipino population was identified.

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Cite this article:

  • Labrague, Leodoro J., and Lynette C. Tan. "Fetal Nasal Bone Length in the Period of 11 and 15 Weeks of Pregnancy in the Filipino Population." American Journal of Medical Sciences and Medicine 1.6 (2013): 110-113.
  • Labrague, L. J. , & Tan, L. C. (2013). Fetal Nasal Bone Length in the Period of 11 and 15 Weeks of Pregnancy in the Filipino Population. American Journal of Medical Sciences and Medicine, 1(6), 110-113.
  • Labrague, Leodoro J., and Lynette C. Tan. "Fetal Nasal Bone Length in the Period of 11 and 15 Weeks of Pregnancy in the Filipino Population." American Journal of Medical Sciences and Medicine 1, no. 6 (2013): 110-113.

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1. Introduction

Screening for chromosomal abnormalities during the 1980s was initially based only on the pregnant woman's age. In the later years, it has been broadened and included maternal serum alpha-fetoprotein, [1] maternal serum biochemical markers [2], and nuchal translucency thickness measurements. [3] Recently, sonographic images of the fetal nose during the second trimester have gained popularity in accurately predicting the risk of the chromosomal birth defect such as Down syndrome. [4, 5].

The fetal nasal bone can be visualized by sonography at 11 to 13+6 weeks of gestation in 99.5% of chromosomally normal fetuses [4]. However, in about 60–70% of fetuses with trisomy 21 and in about 2% of chromosomally normal fetuses the nasal bone is not visible at 11-13 weeks' gestation due to delayed ossification or hypoplasia. [4] Few other studies reported that absence of nasal bone by first trimester ultrasound was significantly associated with Down syndrome. Otano et al [6] reported absence of fetal nasal bone in 60% of fetuses with Down syndrome, while Orlandi et al. [7] observed absence of fetal nasal bone in 67% of fetuses with trisomy 21 and 1% in chromosomally normal fetuses. Prefumo et al [13] also showed a trend of a higher incidence of an absent nasal bone in fetuses of healthy Asian mothers. Moreover, hypoplasia and absence of the nasal bone were also reported in 36% and 2.5% respectively in aborted fetuses. [8] Furthermore, if combined with other screening methods such as maternal serum free beta-human chorionic gonadotropin (B-hCG), maternal age, fetal nuchal translucency (NT) thickness, and pregnancy-associated plasma protein (PAPP-A) at 11 – 14 weeks, it is projected to increase detection rate to 85% with a false-positive rate of 5% [4].

It is essential to note that nasal bone length measurement is impacted by race and ethnicity. Therefore, racial adjustment is needed in the measurement of fetal nasal bone in screening for trisomy 21 during pregnancy [15].

Reference values for nasal bone length have been reported in different countries and ethnic populations [9, 10, 11, 12, 14, 18]. However, to the authors’ knowledge, no study ascertaining reference ranges for the nasal bone length in a Filipino population have been carried out. Thus, this prospective, cross-sectional study was conducted to establish reference values for the nasal bone length (NBL) at 11 – 15 weeks of gestation in the Filipino population.

1.1. Research Objective

This study was conducted to establish reference values for the nasal bone length (NBL) at 11 – 15 weeks of gestation in the Filipino population.

2. Methodology

This prospective, cross-sectional study was conducted in the clinical division of the department of Obstetrics and Gynecology at the University of Santo Tomas Hospital, Philippines during the months of August 2010 to January 2011.

The study sample included 74 pregnant women who had been submitted for first trimester ultrasound scanning. For the purpose of this study, inclusion criteria were set for the purpose of delimitation such as; (a) women with singleton pregnancy, (b) gestational age of 11 to 14 based on the last menstrual period and as confirmed in the ultrasound, and (c) absence of malformations or pregnancy complications. The study protocol was approved by the Ethics Committee of the University of Santo Tomas Hospital.

In measuring the nasal bone length, a sagittal section of the fetal profile was obtained with the ultrasound transducer at an angle between 45 to 135 to the facial plane. The image was magnified so that the fetal head and upper thorax were present on the 75% of the screen. The nasal bone and nasofrontalsynostosis, which appear as an anechoic area on the glabellar region, were identified besides other two liner parallel and echogenic images corresponding to the skin interface right above the nasal bone. Once the appropriate plane was identified, measurement of the nasal bone was performed. The correct plane for the measurement of the fetal nasal bone length is illustrated in Figure 1.

Figure 1. Measurement of the fetal nasal bone length

All the sonographic examinations were performed in GE Voluson 750 equipment coupled with a convex transducer (3.5 – 5.0 MHz) and the trans-abdominal approach was adopted for all the measurements.

Following data collection, statistical analysis was performed using Microsoft Excel and were computed by SPSS version 19. Scatter plots for nasal bone length as a function of gestational age and crown rump length were constructed. The 5th, and 95thpercentile values were calculated for each gestational week. Logistic Regression analysis was done to identify correlations between nasal bone length, gestational age, and crown rump length.

3. Results

Fetal nasal bone length measurement was successfully performed in all 74 cases. The fetal nasal bone was visualized and measured in 100% of the fetuses. The average maternal age was 28.5 years with standard deviation of 5 years. The mean nasal bone length was 2.64 mm with an overall SD of 0.86 mm.

Table 1 shows the average means, standard deviations, and reference measurements in the 2.5%, 5%, 50%, 95%, and 97.5% percentiles for fetal nasal bone length during the period of 11th to 15th weeks of gestational age. As observed, the nasal bone lengths were 1.97, 2.37, 2.90, 3.49, and 4.05 between 11th, 12th, 13th, 14th, and 15th gestational weeks respectively. Table 2 presents nasal bone length in the first trimester in different ethnic groups.

Figure 2 shows the linear relationship between NBL and GA. The nasal bone length increased significantly with gestational age (P = .01). The nasal bone length increased linearly with advancing gestational age and was described by the following equation: y=0.518 x – 3.776 (R2 = 0.738). When the regression analyzes of relationship between nasal bone and CRL was done, regression equation was found as: y=18.50 x + 13.14 (R2 = 0.811) (Figure 3). Also, statistically a significant correlation was found between gestational age and CRL (Figure 4).

Table 1. Nasal Bone Length in the First Trimester

Table 2. Nasal Bone Length in the First Trimester in Different Ethnic Groups (5% and 95% percentile)

Figure 2. Scatter plot between nasal bone length and gestational age
Figure 3. Scatter plot between nasal bone length and crown rump length
Figure 4. Scatter plot between gestational age and crown rump length

4. Discussions

This prospective, cross-sectional study was established reference values for the nasal bone length (NBL) at 11 – 15 weeks of gestation in the Filipino population. Reference values for nasal bone length have been reported in different countries and ethnic populations. In the current study, the mean nasal bone length ranged from 1.97 mm to 4.05 mm. When compared with other ethnic groups [9, 10, 12, 14], nasal bone length in Filipino population appears to be longer. For instance, in the Korean population, the average nasal bone length were 1.5 mm and 2.1 mm for 11 and 14 weeks gestation [9] The NBLs at the 50th percentile in Latin American population were 1.5, 1.7, and 1.9 mm at 11, 12, and 13 weeks of gestation, respectively. [10] Meanwhile, the nasal bone length in Thai fetuses at 11 to 15 weeks were 1.4 mm (range, 1.1-1.9), 1.7 mm (range, 1.1-2.5), and 2.1 mm (range, 1.5-2.6) at gestational age of 11, 12, and 13 weeks respectively [18]. In the Turkish population, the median values of nasal bone lengths were 1.7 mm, 1.9 mm, and 2.2 mm for 11, 12 and 13 gestational weeks respectively. [12] In the study developed by Cossi et al [14] in a Brazilian population, the nasal bone length in all cases ranged between 1.69 mm and 2.94 mm at 11th and 15th weeks. It can be gleaned further that the average values for nasal bone measurements vary from one study to another. In our study, the mean NBL during the 11th to 15th weeks were relatively higher compared to previous studies undertaken [9, 12, 14, 18]. It is essential to note therefore, based on the previous findings that race and ethnicity have an impact on fetal nasal bone length. In agreement with previous authors [15], maternal ethnicity should be required for utilizing the fetal nasal bone length in the screening for trisomy 21 at the first trimester of gestation. However, other factors such as observer variability and quality of machine used should not be undermined.

It was also evident that the nasal bone length in all cases was increased linearly as pregnancy advances. This result is in keeping with the result obtained by Ceciro et al [4] Cossi et al [14], Moon et al [9], Yayla et al [12], Chen et al. [16], and Cusick et al [17]. Nasal bone length was also highly correlated with CRL. It can be concluded based on this result that as pregnancy progresses, measurements of nasal bone length becomes easier and feasible.

While these data are important as it is the first analysis conducted in the country, nevertheless it has some limitations. First, this investigation was conducted among pregnant women from one province only, thus exclusion of pregnant women from other provinces may limit the generalizability of this investigation. Secondly, the small sample size might have affected the statistical power and effect size of the study. Thus, future studies utilizing bigger samples may be conducted to increase statistical power and effect size.

5. Conclusion

Despite of the limitations posed by this investigation, our findings provided reference values for the nasal bone length (NBL) at 11 – 15 weeks of gestation in the Filipino population. Findings also revealed that nasal bone length in the samples vary from other race and ethnic group. In agreement with previous authors, examination of fetal nasal bone at 11 – 15 weeks could have major implications in screening for trisomy 21 by maternal age and fetal nuchal translucency. The findings added knowledge to the existing body of literature on research related to trisomy 21 screening during pregnancy.

Competing Interest

The author(s) declare that they have no competing interests.

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