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Lung Diameter Measurement (Fetal Ultrasound)

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

This test measures the size of a baby’s lungs during pregnancy using ultrasound. It helps assess lung development, often performed between 24 and 36 weeks.

Quick summary

["This test helps track lung growth and identify potential developmental concerns early."]

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

Key facts at a glance

LOINC
53672-2
Short code
Fet Lung-R Diam US.meas
Synonyms
Fet Lung-R Diam 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?

Your healthcare provider may recommend this test if you’re at higher risk for complications, such as preterm labor, or if you’re experiencing symptoms like shortness of breath or irregular fetal movement. It can also be part of routine prenatal care to monitor fetal health.

What Happens During the Test?

You’ll lie on an exam table while a technician applies a gel to your abdomen. A handheld ultrasound probe is gently placed on your skin to create images of your baby’s lungs. The test usually takes about 15–30 minutes and is painless.

What Are the Possible Results?

Results are interpreted by comparing the measured lung diameter to standard fetal growth charts. Smaller-than-expected measurements may signal concerns about lung development, while larger measurements could indicate other factors like polyhydramnios (excess amniotic fluid).

What Does This Test Tell Us About My Health?

While this test focuses on fetal lung development, it doesn’t diagnose medical conditions in you. It helps ensure your baby’s organs are developing properly and may prompt further testing if needed, such as additional ultrasounds or fetal monitoring.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Fetal Lung Diameter

Frequently asked questions

What questions might I have about this test?
This test is typically non-invasive and doesn’t require preparation. If you have questions about discomfort or timing, ask your healthcare provider. Results are usually reviewed within 1–2 weeks, but timing varies by clinic.
Will I need to do anything before or after the test?
You can eat, drink, or move normally before the test. Avoid full bladder if possible, as it may interfere with imaging. No special aftercare is needed, but follow up with your provider if you have concerns about your baby’s movement or your symptoms.
Could this test affect my pregnancy plans?
Not directly. However, if results suggest developmental concerns, your provider may discuss additional steps, such as closer monitoring or specialized care. Always trust your healthcare team’s guidance.
  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