LIMITED EFFECTIVENESS OF FEMUR AND HUMERUS SHORTENING AS MARKERS OF DOWN-SYNDROME IN EARLY MIDTRIMESTER FETUSES

This is a prospective screening Study addressed to assess the value of femur and humerus shortening in the prenatal detection of Down syndro me. Prior to amniocentesis, 1,543 consecutive pregnancies between 13 a nd 18 weeks were studied. Femur and humerus shortening were assessed w ith the use of 6 different ratios, and then correlated with the karyot ype obtained in amniotic fluid. Sensitivities achieved for Down syndro me with femur ratios were lower than those using humerus (17-22 vs. 43 %) for similar false-positive rates (7-8 vs. 6-8%). The most effective ratio was the observed-to-expected humerus length with 43% sensitivit y for a 6% false-positive rate. Combining femur and humerus measuremen ts did not substantially improve the prediction obtained using the bes t humeral ratio. In conclusion, femur and humerus shortening appears t o be of limited value in the detection of Down syndrome.