Antenatal diagnosis of short-limb dwarfism: sonographic approach

Based on the findings in 12 patients with skeletal dysplasia diagnosed antenatally, the authors propose a tailored approach to the evaluation of foetuses with shortened long bones, depending on the time of discovery, the degree of shortening and the associated findings. During the second trimester, a very short femur [2 standard deviations (SD) - 5 mm and less] most probably corresponds to a bone dysplasia, although the differential diagnosis is mainly early intra-uterine growth retardation, and the foetal skeleton should be surveyed completely in order to find supplementary features suggestive of dwarfism. Anomalies of long bones in their shape, thickness or contour, or spinal ossification disorders or undermineralisation (best evaluated at the level of calvarial bones) are most helpful in determining the type of dysplasia. A short femur (between 2 SD and 2 SD - 4 mm) may indicate growth retardation, a chromosomal anomaly or dwarfism. Follow-up examinations are mandatory in order to differentiate between them. During the third trimester a very short femur may indicate a bone dysplasia and the work-up should be the same as in the second trimester. A short femur may correspond to dwarfism of late development, a growth-retarded foetus or constitutional shortness. Various ratios, especially that of the femur/foot, are helpful in differentiating between them. In case of previous family history, a short or very short femur usually indicates recurrence of the dwarfism. In all cases of antenatal diagnosis, confirmation of the sonographic findings should be obtained either by foetal or neonatal radiographs. The approach proposed by the authors should provide sufficient information to counsel the family not only for the ongoing pregnancy but also for subsequent ones.