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Fetal Femur Length from Gestational Age (Summative Measurement)

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

This test measures the length of the fetal femur bone using ultrasound to estimate gestational age. It helps confirm how far along in pregnancy you are.

Quick summary

["This test helps confirm pregnancy progress and monitor fetal development."]

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

Key facts at a glance

LOINC
33165-2
Short code
Fet Femur Length from GA.ASUM00
Synonyms
Fet Femur Length from GA.ASUM00
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-estimated-from-asum
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?

Your healthcare provider may order this test if you have concerns about your due date, if early ultrasound results are unclear, or if you’re at risk for complications like preterm labor. It’s also used to track fetal growth when other methods suggest potential delays.

How Is the Test Performed?

A trained ultrasound technician places gel on your abdomen and uses a handheld device to capture images of your fetus’s bones. The technician measures the femur length and compares it to standard reference ranges for your gestational age.

What Does the Result Mean?

The result is used to estimate your due date or assess fetal growth. If the measurement is shorter than expected, it may indicate a potential pregnancy complication that requires further evaluation. If longer, it might suggest an advanced gestational age.

Common Reasons for Testing

This test is often performed during the first trimester (around 10–14 weeks) to confirm viability and estimate due dates. It can also be repeated later in pregnancy if needed for monitoring.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Fetal femur length is a key biomarker in early pregnancy screening. Abnormal measurements may signal conditions like intrauterine growth restriction, chromosomal abnormalities, or other fetal concerns. It’s typically part of a broader evaluation rather than a standalone diagnosis.

Short name

Fetal Bone Length Assessment

Frequently asked questions

What happens if my result is different from expected?
If your result is outside the typical range, your healthcare provider will discuss next steps, which may include additional ultrasounds, further testing, or monitoring to ensure your pregnancy progresses healthily.
Do I need to prepare for this test?
No special preparation is needed. You can eat, drink, or move as usual. Wear comfortable clothing with a loose waistband for the ultrasound.
How soon will I get my results?
Results are usually available immediately during the ultrasound or within a few days. Your provider will explain them in detail during your follow-up visit.
  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