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A Thai Reference for Normal Fetal Nasal Bone Length at 15 to 23 Weeks’ Gestation

Department of Obstetrics and Gynecology (S.S., T.S., C.S., O.K.) and Epidemiology Unit (A.G.), Faculty of Medicine, Prince of Songkla University, Hat Yai, Thailand.

Address correspondence to Thitima Suntharasaj, MD, Department of Obstetrics and Gynecology, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla 90110, Thailand. E-mail: krataja{at}yahoo.com

Objective. The purpose of this study was to establish a Thai reference for normal fetal nasal bone length at 15 to 23 weeks’ gestation. Methods. The fetal nasal bone was measured by sonography in 295 pregnant women at 15 to 23 weeks’ gestation from May to August 2005. One of the first 4 authors performed 3 measurements for each woman when the fetus was in the midsagittal plane and the nasal bone was close to a 45° or 135° angle to the ultrasound beam. All neonates were examined after delivery to confirm an absence of congenital abnormalities. Results. The median nasal bone length increased by gestational age from 3.6 mm at 15 weeks to 7.3 mm at 23 weeks in a linear relationship. The fifth percentile nasal bone lengths were 2.5, 3.04, 3.28, 3.64, 4.21, 4.82, 5.69, and 6.13 mm at 15, 16, 17, 18, 19, 20, 21, and 22 weeks, respectively. The median time for measurement was 5 minutes. Conclusions. The nasal bone length in Thai fetuses at 15 to 23 weeks was found to be on average shorter than that in white and African American fetuses.

Key Words: fetal nasal bone • normal length • Thai reference