Fetal Radius Length (Longest Bone)
This test measures the length of the longest radius bone in a fetus, which helps assess fetal bone development during prenatal ultrasound examinations.
["This measurement supports early detection of potential growth or skeletal abnormalities."]
Key facts at a glance
- LOINC
- 11973-5
- Short code
- Fet Radius Length Est from GA.Merz87
- Synonyms
- Fet Radius 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?
Your healthcare provider may order this test as part of a routine ultrasound during pregnancy to monitor fetal development, especially in the second trimester. It can help identify conditions that might affect bone growth or overall fetal health.
How Is the Test Performed?
The test is conducted during an ultrasound, where a transducer sends sound waves to create images of the fetus. The provider measures the longest radius bone in the fetus’s forearm, which is typically visible by around 16 to 22 weeks of gestation.
What Does the Result Mean?
While specific reference ranges vary by gestational age, deviations from expected measurements may indicate potential concerns such as chromosomal abnormalities, genetic disorders, or other growth-related issues. Your provider will discuss findings in the context of your pregnancy and overall health.
What Are Possible Outcomes?
Results may fall within normal ranges, fall below (smaller than expected), or fall above (larger than expected) typical measurements. Below-average lengths might prompt further evaluation, while above-average lengths are less commonly associated with immediate concerns but should still be reviewed by your healthcare team.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Fetal radius length is part of a broader assessment of fetal skeletal development. Abnormal measurements may signal underlying conditions that require additional diagnostic testing, such as genetic counseling or further imaging. Early detection allows for timely interventions if needed.
Short name
Fetal Bone Measurement
Frequently asked questions
What does a low fetal radius length indicate?
How often is this test repeated during pregnancy?
Can diet or lifestyle affect fetal bone measurements?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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