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Fetal Femur Length Measurement (Ultrasound)

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

This test measures the length of a baby’s femur bone using ultrasound during pregnancy to assess fetal growth.

Quick summary

["Ultrasound measurements help track fetal development and detect potential growth concerns early."]

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

Key facts at a glance

LOINC
11963-6
Short code
Fet Femur Length US.meas
Synonyms
Fet Femur 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

Why Is This Test Done?

Doctors may order this test if you’re at higher risk for complications like preterm birth, intrauterine growth restriction (IUGR), or other pregnancy-related issues. It’s also used to monitor fetal growth in cases of known or suspected growth delays.

What to Expect During the Test

You’ll lie on an exam table, and a technician will apply a warm gel to your abdomen. A handheld device (transducer) will glide over your skin to capture images of your baby’s femur. The process is painless and typically takes about 15–30 minutes.

How the Results Are Used

The measured femur length is compared to standard growth charts for your baby’s gestational age. Small variations may be normal, but significant differences could signal the need for further evaluation, such as additional ultrasounds or fetal monitoring.

Common Reasons for Testing

This test is often part of routine prenatal care to ensure your baby is growing appropriately. It may also be performed if you have risk factors like chronic hypertension, diabetes, or a history of preterm labor.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Fetal femur length is a reliable marker of fetal growth and development. Low measurements may indicate intrauterine growth restriction (IUGR), while high measurements could raise concerns about placental insufficiency or other conditions. Early detection allows for timely interventions, such as changes in medication, increased prenatal care, or delivery planning.

Short name

Femur Length

Frequently asked questions

What does a low or high femur length mean?
A low femur length may suggest slower fetal growth, which could be due to conditions like IUGR or other pregnancy complications. A high length might be less common but could warrant further investigation to rule out issues like placental problems.
Is this test painful?
No, this ultrasound test is completely painless. You may feel a slight pressure or warmth from the gel, but there’s no discomfort.
How often is this test repeated?
The frequency depends on your pregnancy and health status. Some women may have this test once or twice during pregnancy, while others may need it more often if they have risk factors or require closer monitoring.
  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