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Fetal Femur Length Measurement (Ultrasound)

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

This test measures the length of a fetus’s femur bone using ultrasound to assess growth and development.

Quick summary

["Ultrasound measurements help monitor fetal development during pregnancy."]

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

Key facts at a glance

LOINC
11970-1
Short code
Fet Femur Length Est from GA.Merz87
Synonyms
Fet Femur Length Est from GA.Merz87
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
estimated-from-gestational-age-merz
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 to check if your baby is growing at the expected rate. It can help identify potential issues with fetal development, such as growth restrictions or chromosomal abnormalities early in pregnancy.

How Is the Test Performed?

You’ll lie on an exam table, and a technician will apply a gel to your abdomen. A handheld device (ultrasound probe) will glide over your skin to capture images of your baby’s bones. The technician measures the femur length on the screen.

What Does the Result Mean?

The measurement is compared to standard fetal growth charts. A result that falls below expected ranges may signal concerns that need further evaluation, such as additional ultrasounds or genetic testing.

What Are Common Reasons for This Test?

Common reasons include first-trimester screening, monitoring high-risk pregnancies (e.g., maternal health conditions), or assessing fetal well-being when other growth measurements are abnormal.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Femur Length

Frequently asked questions

What does a low femur length mean?
A lower-than-expected femur length may raise concerns about potential growth restrictions or genetic factors. Your healthcare provider will discuss next steps, such as additional ultrasounds or further testing, based on the result.
Is this test painful?
No, the ultrasound is completely painless. You may feel a slight pressure or warmth from the gel and probe, but no discomfort.
How often is this test repeated?
The frequency depends on your pregnancy status. It may be done once or multiple times, especially if your pregnancy is considered high-risk or if earlier measurements were concerning.
  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