Investigation of the Distribution of Fetal Nasal Bone Percentile Values in First-Trimester Fetal Anomaly Screening

INTRODUCTION: We aim to determine the fetal nasal bone length (NBL) percentile values that can be used in the prediction of the fetal anomaly at 11-14 weeks of gestation in a low-risk population. METHODS: Our prospective and cross-sectional study included four hundred and eighty-six singleton pregnancies who applied for the first-trimester aneuploidy screening test at 11-14 weeks of gestation. We excluded pregnant women with fetal structural or chromosomal anomaly, nuchal translucency >3mm, an absent nasal bone, and in utero fetal death. Reference and percentile values of the NBL were calculated separately for 11,12,13,and 14. gestational weeks. RESULTS: Standard NBL measurements were performed in 486 pregnancies according to inclusion and exclusion criteria. Median NBL values were computed for each gestational age (GA), for 11,12,13 and 14. weeks of gestation was found 1.6mm (range=1.1-2.5), 1.8mm (range=1.1-3.0), 2.0mm (range=1.4-3.1), and 2.2mm (range=1.7-2.8), respectively. A positive significant correlation was found between NBL and the crown-rump length (CRL) (NBL (mm) = [0.02xCRL(mm)] + 0.73, r=.483; p<.001). The 5th percentile of NBL for GA was calculated, for 11,12, 13, and 14. weeks of gestation was found 1.2mm,1.4mm,1.5mm, and 1.7mm respectively. DISCUSSION AND CONCLUSION: We revealed the reference value of NBL for each gestational week in the first trimester of the low-risk population. The data obtained in our study can be used in the screening of genetic syndromes, especially Down syndrome, associated with nasal bone hypoplasia. Our reference value of NBL for the first trimester in singleton pregnancy varies from both previous racial and ethnic groups studies, and other Turkish studies