Femur/foot length ratio for detection of Down syndrome: results of a multicenter prospective study. The Association Française pour le Dépistage et la Prévention des Handicaps de l'Enfant Study Group.
OBJECTIVE
The aim was to determine the sensitivity and specificity of a short femur for detection of trisomy 21 in the second trimester.


METHODS
Thirty-six investigators in 12 centers measured biparietal diameter and femur and foot lengths in 3582 14- to 24-week-old fetuses in mothers undergoing amniocentesis for age, history of genetic disorder, or laboratory signs.


RESULTS
Among the various ratios for evaluating femur shortening the femur/foot ratio appeared to be the most discriminatory. At an upper cutoff level of 0.88 a sensitivity of 35% was obtained for 4.6% false positives in normal infants. However, to only obtain 2.3% false positives, the cutoff limit had to be set at 0.85, giving a sensitivity of no more than 15%.


CONCLUSIONS
Determination of the femur/foot ratio improves ultrasonographic detection of trisomy 21 in the second trimester, although for systematic use it would lead to an unacceptable number of unnecessary amniocenteses.
Grandjean
H
H
Institute National de la Santé et de la Recherche Médicale, Université Paul Sabatier, Toulouse, France.
Sarramon
M F
MF
D000649:Amniocentesis; D004314:Down Syndrome / Q000175:diagnosis* / Q000000981:diagnostic imaging; D005189:False Positive Reactions; D005260:Female; D005269:Femur / Q000033:anatomy & histology*; D005315:Fetal Diseases / Q000175:diagnosis*; D005528:Foot / Q000033:anatomy & histology*; D006801:Humans; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal