Femur length (obstetric ultrasound)

Last revised by Jeremy Jones on 6 Apr 2023

Citation, DOI, disclosures and article data

Citation:

Stanislavsky A, Jones J, Loomba S, et al. Femur length (obstetric ultrasound). Reference article, Radiopaedia.org (Accessed on 10 Dec 2023) https://doi.org/10.53347/rID-26433

DOI:

https://doi.org/10.53347/rID-26433

Permalink:

https://radiopaedia.org/articles/26433

rID:

26433

Article created:

21 Dec 2013, Alexandra Stanislavsky

Disclosures:

At the time the article was created Alexandra Stanislavsky had no recorded disclosures.

View Alexandra Stanislavsky's current disclosures

Last revised:

6 Apr 2023, Jeremy Jones ◉

Disclosures:

At the time the article was last revised Jeremy Jones had no financial relationships to ineligible companies to disclose.

View Jeremy Jones's current disclosures

Revisions:

9 times, by 7 contributors - see full revision history and disclosures

Systems:

Obstetrics

Sections:

Approach

Tags:

stub, cases

Synonyms:

Femur length (FL)
Femoral length
Femoral lengths
Femur diaphysis length
Femur length

Fetal femur length (FL) is a basic biometric parameter to assess fetal size. Femur length, together with biparietal diameter, head circumference, and abdominal circumference, are computed to produce an estimate of fetal weight. In the second trimester, this may be extrapolated to an estimate of gestational age and an estimated due date (EDD).

Femur length can be used to calculate fetal length, another predictor of fetal growth, with the following equation ³:

Fetal length in centimeters = 6.18 + 0.59 x femur length in millimeters.

Measurement criteria:

measure with the transducer aligned along the long axis of bone - perpendicular to the shaft
measure where the ends of the bones are blunt and not pointed.
measure from the blunt end of the proximal femoral epiphysis to the blunt end of the distal femoral epiphysis
measure post 32-34 weeks when the distal femoral epiphysis can be seen (although not measured)
never measure when there is excessive bowing, demineralization or shortened length