HUMERUS AND FEMUR LENGTH IN FETUSES WITH DOWN-SYNDROME

The aim of the study was to assess the value of sonogaphic measurement of fetal humerus and femur lengths in the second trimester as a scree ning tool for Down syndrome (DS). We reviewed retrospectively fetal so nographic biometry made at the time of amniocentesis between 15 and 19 weeks. The study group consisted of 27 DS fetuses. The control group comprised 500 normal fetuses chosen randomly. The expected humeral and femoral lengths for a given biparietal diameter were estimated by lin ear regression equations from the 500 normal fetuses. Receiver operati ng characteristic curve analysis was performed to evaluate both the de tection rate and the false-positive rate of different cut-off values o f measured to expected lengths ratios. The median femur and humeral le ngths in DS fetuses were 0.91 times the expected values. No significan t differences in the detection rate and false-positive rate were found between the humerus and femur lengths. When the humeral and femoral l engths were combined, we observed a remarkable reduction in the false- positive rate. A measured to expected length ratio of 0.91 detected 44 .4 per cent of DS fetuses with 7.6 per cent false positives. These res ults suggest that the combination of femoral and humeral lengths may p ermit a more efficient use of ultrasound in screening for Down syndrom e than the use of either alone.