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Soft Markers
Short Femur Length

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Femur length less than the third centile.


The femur is the longest bone and is measured as part of the routine mid pregnancy anomaly scan. The distribution of limb length in a population of fetuses will vary, but some will be considered small. The definition used above allows for local criteria and individual customisation.

Standard image for identification/exclusion and technique for measurement/assessment

The femur should be measured with the femur perpendicular to the ultrasound beam and with the epiphyseal cartilages visible on the image. The epiphyseal cartilages should not be included in the measurement. Vertical measurement will foreshorten the result due to increased velocity of ultrasound in dense structures.

The ultrasound assessment should be completed, looking in particular for the other soft markers: nuchal pad, echogenic bowel, echogenic foci, renal pyelectasis and choroid plexus cysts.

Implication of a positive finding in isolation

This may be indicative of a general skeletal malformation (Reference1) or growth problem. A full long-bone survey and examination of the fetal chest should be performed. The foot length is useful in interpretation of long bone measurement (Reference2). Lethal malformations may be associated with a small chest, which causes pulmonary hypoplasia.

Further management of an isolated short femur may include growth assessment with ultrasound later in pregnancy.

There is a weak association with trisomy 21 in conjunction with other markers, but in isolation no further action is required.

Image 4 - Short Femur length



1. Gonclaves L, Jeanty P. Fetal biometry of skeletal dysplasias: a multicentre study. Journal of Ultrasound in Medicine. 1994;13(12): 977-85, Abstract

2. Grandjean H, Sarramon MF. Femur/foot length ratio for detection of Down syndrome: results of a multicentre prospective study. The Association Francaise pour le Depistage et la Prevention des Handicaps de l’Enfant Study Group. American Journal of Obstetric & Gynecology. 1995; 173(1): 16-9, Abstract


© Perinatal Institute 2011