Nasal Bone Hypoplasia in Trisomy 21 at 15 to 24 Weeks’ Gestation in A High Risk Thai Population
Bongkoch Naraphut MD*, Boonchai Uerpairojkit MD*, Surasith Chaithongwatthana MD*, Yuen Tannirandorn MD*, Somchai Tanawattanacharoen MD*, Saknan Manotaya MD*, Dhiraphongs Charoenvidhya MD*
Affiliation : * Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Faculty of Medicine, Chulalongkorn University
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.
Materials and Methods : 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 measure-
ments 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.
Keywords : Nasal bone, Nasal bone hypoplasia, Biparietal diameter/nasal bone length ratio, Trisomy 21, Down syndrome
