Outcome of fetuses with diagnosis of isolated short femur in the second half of pregnancy

Abstract

Objectives. To assess the outcome of fetuses with isolated short femur detected at 19-41 weeks and determine to what extent this incidental finding should be a cause of concern in fetuses with a normal previous follow-up. Methods. 156 fetuses with isolated short femur were compared with a control group of 637 fetuses with normal femur length. FL values were converted into Z-scores and classified into 4 groups: control group: Z-score over -2, group 1: Z-score between -2 and -3, group 2: Z-score between -3 and -4, and group 3: Z-score below -4. FL values were plotted with the curves representing Z-scores -2, -3, and -4. To assess fetal outcome, the frequency of SGA, IUGR, abnormal umbilical Doppler (AUD), Down's syndrome, and skeletal dysplasia was determined for each group after delivery, and the relative risk in comparison with the control group was obtained. Finally, ROC curves were drawn in order to evaluate the FL diagnostic ability for the conditions appearing with increased frequency. Results. SGA, IUGR, and AUD were more frequent in the fetuses with short femur. Conversely, none of them presented Down's syndrome or skeletal dysplasia. According to ROC analysis, FL measurement behaved as a good diagnostic test for SGA and IUGR. Conclusions. A short femur diagnosis in a fetus with an otherwise normal follow-up determines just a higher risk of being small (SGA or IUGR).

Figure 1

Scattergram of FL values depicted according to the Z-score classification. Roundels: fetuses with FL Z-score over −2, squares: fetuses with FL Z-score between −2 and −3, clear triangles: fetuses with FL Z-score between −3 and −4, and dark triangles: fetuses with FL Z-score below −4. Curves represent Z-scores −2, −3, and −4.

Figure 2

Receiver-operating characteristic (ROC) curves representing the diagnostic ability of the FL Z-score for the diagnosis of the three conditions associated with femur shortening (SGA, IUGR, and AUD). AUC: area under the curve.