Ultrasound fetal femur length measurement in the screening for Down's syndrome

Abstract

Summary: The fetal femur length determined by an ultrasound examination at between 13 and 39 weeks gestation in 83 pregnancies associated with Down's syndrome was statistically significantly less than the expected value for pregnancies with the same biparietal diameter examined in the same ultrasound department (P<0.0001). Expected values were based on linear regressions of femur length on biparietal diameter in 1340 control pregnancies from 27 ultrasound departments. The median value for the affected pregnancies was 0.94 times the expected value (95% CI 0.92 to 0.97). Eleven per cent of affected and 14% of control pregnancies had values ≤0.85 times the expected. The reduction in femur length in affected pregnancies was not related to biparietal diameter or to maternal age. Fetal femur length may be useful as an ancillary screening variable in the antenatal screening for Down's syndrome.