To establish the reference range of fetal nasal bone length (NBL) in the second trimester in the Korean population and to determine its clinical value in screening for trisomy 21.Study Design
A total of 3019 consecutive fetuses at 16-28 weeks of gestation underwent ultrasonographic measurement of NBL at Asan Medical Center from October 2003 to August 2005.Results
Fetal profile was successfully examined in 95.6% (2885/3019) of the fetuses. NBL increased linearly with advanced gestation (R2 = 0.4337, p < 0.001). During this period, 23 fetuses with chromosomal abnormalities (including nine with trisomy 21, two with trisomy 18, and three with Turner syndrome) were detected. In trisomy 21, hypoplastic nasal bone (<2.5th percentile) was seen in 3/9 fetuses, and the NBL of one fetus was between the 2.5th and 5th percentile. Hypoplastic nasal bone was seen in 3.1% (89/2833) of fetuses with normal chromosomal or postnatal examination findings.Conclusion
We present the normal range of NBL in the second trimester in the Korean population and also their linear relationship with gestational age (GA). The NBL appears to be shorter in Korean fetuses than Caucasian and Chinese fetuses. This indicates that the normal range would vary between races and that a relative percentile is a more reliable screening criterion than an absolute value.