A prospective cross-sectional study to define racial variation in fetal nasal bone length through ultrasound assessment at 18-20 weeks' gestation.
OBJECTIVE
An absent or short nasal bone is highly predictive of Down syndrome in Caucasian populations, but Asians may have shorter nasal bones - increasing the false positive rate of screening. We examine differences in nasal bone length (NBL) in Caucasian and Asian populations.


METHODS
This prospective cohort study involved pregnant women attending for their routine anomaly scan at 18-20 weeks' gestation. Ethnicity of the patient and their partner was recorded, and the nasal bone was measured three times. Mean NBL was calculated and used to investigate the effect of ethnicity first with a simple linear regression model and second with a mixed-effects regression model that accounted for variability of measurement between sonographers.


RESULTS
A total of 1087 families were involved in the study, including 592 (54%) Caucasians, 214 (20%) East Asians, 110 (10%) South Asians and 171 (16%) West Asians. Twenty-three sonographers performed the scans with an average of 19 scans each. There is no significant difference in NBL between Caucasian and Asian populations. The mixed-effects model shows that accounting for sonographer variation is important, with 6.7% of the total variance in measurement being related to this random effect.


CONCLUSIONS
There is no significant difference in NBL between Caucasian and Asian populations. It is reasonable to use criteria established in a Caucasian population to define the characteristics of an absent/short nasal bone in Asian fetuses. This finding also removes difficulties in counselling mixed race couples.
Department of Obstetric and Gynaecological Ultrasound, Royal Prince Alfred Hospital, Sydney, New South Wales, Australia.
Ritu
R
Mogra
Philip J
PJ
Schluter
Robert F
RF
Ogle
Justine
J
O'Connell
Lou
L
Fortus
Jon A
JA
Hyett
D000293:Adolescent; D000328:Adult; D044466:Asian People / Q000706:statistics & numerical data; D003430:Cross-Sectional Studies; D004314:Down Syndrome / Q000000981:diagnostic imaging* / Q000208:ethnology; D005260:Female; D006801:Humans; D008875:Middle Aged; D009295:Nasal Bone / Q000000981:diagnostic imaging* / Q000196:embryology; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal; D044465:White People / Q000706:statistics & numerical data; D055815:Young Adult