Improving the consistency and reproducibility of first-trimester nasal bone assessment - a new classification in a low-risk population

Sep 30, 2026

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The study addresses limited reproducibility in fetal first-trimester nasal bone assessment, where “absence” (NBA) relies on subjective definitions. It evaluates a stricter NBA classification defined as complete non-visualization, aiming to increase agreement between nuchal translucency (NT) and retronasal triangle (RNT) ultrasound views. In 354 low-risk singleton pregnancies, reliability and cross-view consistency were analyzed with Cohen’s Kappa and Phi coefficients, and agreement rates compared using McNemar’s test.

LanguageEnglish

CategoryHealthcare

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Pages9

Reading Time23 min

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Abstract

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What’s already known about this topic?

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Song et al. BMC Pregnancy and Childbirth (2026) 26:28 [https://doi.org/10.1186/s12884-025-08529-5](https://doi.org/10.1186/s12884-025-08529-5) BMC Pregnancy and Childbirth RESEARCH Open Access Improving the consistency and reproducibility of first-trimester nasal bone assessment: a new classification in a low-risk population Wen-Ling Song 1,2, Hai-Ou Ma3, Lei Han3, Hong-Ran Li3, Ming-Yu Cui3, Qi-Wei Yang4, Qiong-Wei Huang5, Li-Ying Zhang6, Xin Xu3, Yu Nan3 and Chen Zhu7* Abstract Background The reproducibility of fetal nasal bone assessment is limited by subjective definitions of its absence (NBA) . This study evaluated a new, stricter classification for NBA (complete non-visualization), aiming to improve consistency between the nuchal translucency (NT) and retronasal triangle (RNT) views. We also assessed the incidence of NBA by this new classification and its associated outcomes in a low-risk population. Methodss In this retrospective study of 354 low-risk singleton pregnancies, the nasal bone was assessed in both NT and RNT views using a new, stricter definition and compared against the traditional definition. Inter-rater reliability and inter-view consistency were evaluated using Cohen’s Kappa (κ) and the Phi coefficient, respectively. The McNemar test was then used to formally compare the agreement rates between the two classification. Results The new classification enhanced assessment consistency. Inter-view consistency improved, with the Phi coefficient rising from 0.268 to 0.497. Moreover, the new classification achieved perfect inter-rater reliability (κ=1 . 0), an increase from the substantial agreement of the traditional classification (κ=0 . 829, 95% CI: 0 .655-1. 000) . However, a direct statistical comparison found no significant difference in the agreement rates between the two methods (McNemar test, p=0 . 500) . Conclusions Our stricter definition of NBA shows promise for enhancing assessment consistency and reproducibility and has the potential to reduce false positives. However, due to the low incidence of NBA in our sample, validation of this new criterion's predictive value for aneuploidy in a large, high-risk population is essential before its clinical adoption. Summary What's already known about this topic? The definition of first-trimester nasal bone absence is inconsistent and subjective, leading to poor agreement between ultrasound views and uncertain clinical interpretation. What does this study add? This study introduces and evaluates a stricter classification for nasal bone absence (complete non-visualization) . This new classification improved consistency between ultrasound views (Phi coefficient increased from 0.268 to 0 .497) and achieved perfect inter-rater reliability (κ=1 . 0), a numerical increase from the *Correspondence: Chen Zhu [chenzhu@fudan.edu.cn](chenzhu@fudan.edu.cn) Full list of author information is available at the end of the article © The Author(s) 2025. Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit [http://creati](http://creati)[veco

FAQs

What limitation in nasal bone assessment motivated the study?

Reproducibility is limited because the definition of nasal bone absence (NBA) is subjective, creating poor agreement between ultrasound views and uncertain interpretation.

How is the new NBA classification defined in this research?

The new classification uses a stricter criterion: complete non-visualization of the nasal bone.

What improvements did the new classification show?

It improved assessment consistency, increasing inter-view consistency (Phi from 0.268 to 0.497) and achieving perfect inter-rater reliability (Kappa = 1.0), although direct comparison of agreement rates showed no significant difference (McNemar p = 0.500).

Sep 30, 2026

Uploaded by Bulrr