Maternal ethnicity and variation of fetal femur length calculations when screening for Down syndrome.
OBJECTIVE
To determine whether current methods for detecting Down syndrome based on fetal femur length calculations are influenced by ethnicity.


METHODS
The study population consisted of all fetuses scanned between 14 and 20 completed weeks' gestation from April 1, 1997, to January 1, 2000. The expected femur length was calculated from the biparietal diameter. The variance from the expected femur length, compared with the biparietal diameter, was calculated, and the mean variations were compared by maternal race. Ethnic-specific formulas for expected femur length were derived by simple regression.


RESULTS
There was a statistically significant difference in femur length in the Asian group compared with all other groups, as well as the white group compared with the black and Asian groups (P < .05). However, there was no significant difference between the black and Hispanic groups or the white and Hispanic groups. The Asian group had the largest variation, with the measured femur length being less than the expected femur length. All groups studied had a mean expected femur length less than the mean measured femur length. On the basis of the ethnic-specific formulas for femur length, there was a significant decrease in patients that would undergo further evaluation for Down syndrome.


CONCLUSIONS
There is a significant difference in the mean expected femur length by biparietal diameter among fetuses in the second trimester with regard to ethnicity. Using ethnic-specific formulas for expected femur length can have a considerable impact on the use of sonographic risk factors for Down syndrome screening. Further data are required for use of femur length as a screening tool in the genetic sonogram.
Kovac
Christine M
CM
Department of Obstetrics and Gynecology, Madigan Army Medical Center, Tacoma, Washington 98431, USA.
Brown
Jennifer A
JA
Apodaca
Christina C
CC
Napolitano
Peter G
PG
Pierce
Brian
B
Patience
Troy
T
Hume
Roderick F
RF
Calhoun
Byron C
BC
D000328:Adult; D001741:Black or African American; D001213:Asian; D004314:Down Syndrome / Q000000981:diagnostic imaging* / Q000208:ethnology; D005006:Ethnicity; D005260:Female; D005269:Femur / Q000196:embryology*; D005865:Gestational Age; D006630:Hispanic or Latino; D006801:Humans; D008403:Mass Screening; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D016216:Ultrasonography, Prenatal; D044465:White People