A Thai Reference for Normal Fetal Nasal Bone Length at 11–13(+6) Weeks Gestation

Abstract

Aim: The purpose of this study was to establish a Thai reference for normal fetal nasal bone length (NBL) at 11–13⁺⁶ weeks gestation. Methods: The fetal nasal bone was measured by sonography in pregnant women at 11–13⁺⁶ weeks gestation. All neonates who showed normal karyotypes were examined after delivery to confirm the absence of congenital abnormalities. Results: A total of 255 pregnant women were recruited. Forty-seven pregnant women were excluded from the analysis because of technically unsatisfactory examination or absent nasal bone and chromosomal abnormalities. The mean ± SD of NBL was 1.79 ± 0.33 mm and increased significantly with crown–rump length (CRL) and gestational age (p < 0.001). The best-fit equation for NBL in euploid fetuses in relation to CRL was: NBL (mm) = (0.030 × CRL (mm)) – 0.016. Conclusion: NBL in Thai fetuses at 11–13⁺⁶ weeks was found to be on average shorter than that in Caucasian, African-American and Chinese populations, but similar to those reported in Korean and Latin-American populations.

The usefulness of volume NT software in measuring the fetal nasal bone at 11 to 13 + 6 weeks of gestation

“…However, in comparison with the second trimester, an accurate measurement of fetal NB at 11 to 14 weeks is more difficult to achieve. Reference charts of NB length are available for different ethnic groups also in the first trimester . NB has been measured mostly by 2D ultrasound at the 11 to 14 weeks scan, but the results on the reproducibility of these measurements are conflicting.…”

“…However, in comparison with the second trimester, an accurate measurement of fetal NB at 11 to 13 + 6 weeks is more difficult to achieve. Normal reference values for fetal NB length at 11 to 13 + 6 weeks of pregnancy have been established using 2D ultrasound among different ethnic groups . The reproducibility of these data has been found to be inadequate by some authors and to vary in accordance with the sonographer experience.…”

Follow Your Nose

“…8 Additionally, as the ontogeny of ossification of the fetal nasal bone differs between populations, ethnicity may also affect the visualization of the fetal nasal bone. 4,9,10 For centers incorporating its assessment into their first-trimester algorithm, fastidious nasal bone assessment according to the criteria developed by the Fetal Medicine Foundation across all populations and gestational ages within the FTS window is essential for accurate Down syndrome risk assessment, as classifying this parameter as absent or uncertain significantly reduces the specificity of combined FTS for Down syndrome. 5,[11][12][13] Given the potential difficulty of nasal bone visualization during the earlier part of this gestational age window, during the study period our Center offered a repeat nasal bone evaluation for patients with CRLs <84.0 mm and an "absent" or "uncertain" (unable to be adequately visualized) nasal bone on initial examination.…”

“…Yet, factors such as maternal body habitus (including increased body mass index [BMI]), unfavorable fetal position, early gestational age, poor acoustic windows, and delayed nasal bone ossification can preclude nasal bone visualization at the time of FTS 8 . Additionally, as the ontogeny of ossification of the fetal nasal bone differs between populations, ethnicity may also affect the visualization of the fetal nasal bone 4,9,10 …”