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: Fetal Femur Length, Ultrasound Measurement

Published: August 9, 2026Updated: August 16, 2026

: A fetal femur length measurement is an ultrasound measurement of the baby's thigh bone used to help assess growth and development during pregnancy.

Quick summary

[": Femur length helps your care team track fetal growth and estimate gestational age."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
53681-3
Short code
Fet Ft-R Length US.meas
Synonyms
Fet Ft-R Length US.meas
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
us-measured
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

: What This Measurement Is

: During a prenatal ultrasound, the sonographer measures the length of the developing baby's femur, the long bone of the thigh. This measurement is recorded in millimeters and compared with expected values for the stage of pregnancy.

: How It Is Done

: The measurement is taken painlessly using the same ultrasound probe used for your routine scan. There is no needle, radiation, or special preparation required, and it is usually part of a standard growth or anatomy scan.

: What the Number Means

: Femur length is one of several measurements, along with head size and belly size, used to estimate fetal age and growth. Your clinician interprets the number together with the other measurements and your pregnancy history rather than looking at it alone.

: Limits of the Test

: Ultrasound measurements can vary slightly depending on the baby's position and the person performing the scan. A single value outside an expected range does not by itself diagnose a problem, and repeat imaging may be recommended.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

: Femur length is a standard component of fetal biometry used to help date pregnancy, screen for growth abnormalities, and support evaluation for conditions affecting skeletal development. Results are always interpreted alongside other ultrasound findings and clinical context.

Short name

: Femur Length

Frequently asked questions

: Does this measurement hurt?
: No. It is obtained with an ultrasound probe on the abdomen or, in some cases, the vagina, and involves no needles or radiation.
: Is an abnormal femur length always a sign of a problem?
: No. Measurements can be affected by the baby's position, scan technique, and normal variation. Your clinician considers all measurements and other findings before drawing conclusions.
: Do I need to prepare for the scan?
: Usually no special preparation is needed for a standard ultrasound, though your clinic may give specific instructions for your appointment.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy