Impact of the angle used in 2D Ultrasonography on the foetal femur diaphysis measurement.

Objective The purpose of this pilot study is to compare the 2D scanning measurement of the foetal femoral diaphysis using anterior or lateral/external incidence at ultrasound. Methods In August 2016, 30 consecutive patients underwent a second trimester morphology ultrasound between 21 and 24 weeks of gestation by a senior sonographist. In each case, the femur length was measured either with an anterior angle, estimating the straight aspect of the diaphysis or with a lateral angle, assessing its curved aspect. The two measures were collected prospectively. The difference between paired measurements was calculated and expressed in percentage (mm) and in percentile. Results The median difference between the two ultrasound angles in terms of femur length was 3,55% and in terms of percentile variation was 17,16. Conclusion An anterior angle of measurement of the femur length seems to allow an optimal measure of the straight and longest aspect of the diaphysis. According to our results, this angle should be considered when scoring the quality of a morphological ultrasound, but further and larger studies should be done to confirm our hypothesis.