Management of Fetus with Short Femur Length

Assessment and Diagnosis

Finding of femur length below the 5th percentile for gestational age warrants further evaluation, as recommended by the American College of Obstetricians and Gynecologists 1, 2
Skeletal dysplasia - many fetuses with skeletal dysplasias fall below the third percentile for bone length measurements in the second trimester, according to the American College of Obstetricians and Gynecologists 3, 4
Racial and ethnic variation - femoral bones may be shorter among Asian participants and longer among Black participants, as noted by the American College of Obstetricians and Gynecologists 3, 4

Perform thorough evaluation and measurement of all appendicular bones compared with nomograms for bone length by gestational age, as recommended by the American College of Obstetricians and Gynecologists 3, 4
Assess for other markers of skeletal dysplasia, including chest-to-abdomen ratio, femur length to abdominal circumference (FL/AC) ratio, presence of micromelia, evidence of hydrops, and decreased mineralization of axial skeleton, as recommended by the American College of Obstetricians and Gynecologists 5, 6
Consider aneuploidy screening if not previously done, as shortened femur has been associated with trisomy 21, according to the American College of Obstetricians and Gynecologists 3, 4
Schedule third-trimester ultrasound examination for reassessment and evaluation of growth, as recommended by the American College of Obstetricians and Gynecologists 3, 4

FL/AC ratio is the single best predictor of lethality in skeletal dysplasias, according to the American College of Obstetricians and Gynecologists 5, 6
Pregnancies with lethal skeletal dysplasia had significantly lower FL/AC ratio and were more likely to have a ratio <0.16 than those with neonatal survival, as noted by the American College of Obstetricians and Gynecologists 6, 8

Accurate measurement of femur length is critical - in cases of bowed limbs, measure the actual length of the femur rather than the linear distance between each end, as recommended by the American College of Obstetricians and Gynecologists 6, 8
Some skeletal dysplasias like achondroplasia may not manifest until the third trimester of pregnancy, according to the American College of Obstetricians and Gynecologists 3, 4
If skeletal dysplasia is confirmed, all infants should be reevaluated as soon as practical after delivery, as recommended by the American College of Obstetricians and Gynecologists 7
Postmortem evaluation is recommended for fetuses from pregnancies terminated due to suspected skeletal dysplasia, according to the American College of Obstetricians and Gynecologists 1, 6