ABSTRACT
OBJECTIVE: To assess the utility of nasal bone hypoplasia in the detection of fetuses with trisomy 21 in the second trimester in a high risk Thai population. MATERIAL AND METHOD: A prospective study involving pregnant women undergoing amniocentesis due to increased risk of aneuploidy from January 2005 to December 2005. Fetal biometry and nasal bone measurements were obtained at the time of amniocentesis. Linear regression model and diagnostic tests were analyzed using the SPSS computer program. RESULTS: A total of 407 fetuses were evaluated. In euploid fetuses, the Nasal Bone Length (NBL) increased linearly with advancing gestational age. Fetuses with Down syndrome had a significantly higher proportion of NBL below the 5th centile when compared with normal fetuses (p < 0.05). The optimal nasal bone threshold associated with trisomy 21 is a BiParietal Diameter/Nasal Bone Length (BPD/NBL) ratio of 10 or greater, yielded a sensitivity of 80%, specificity of 86% for detection of trisomy 21. CONCLUSION: Nasal bone hypoplasia is associated with an increased risk of Down syndrome in the presented population.