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Fetal Head Circumference (from Gestational Age Assessment)

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

This test measures the estimated size of your baby’s head based on how far along you are in pregnancy. It helps track fetal growth and development.

Quick summary

Your provider uses this measurement to monitor your baby’s progress during pregnancy.

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

Key facts at a glance

LOINC
33172-8
Short code
Fet Head Circum from GA.ASUM00
Synonyms
Fet Head Circum 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?

Doctors may order fetal head circumference during prenatal visits to check if your baby is growing at a healthy rate. It can help identify potential issues like growth restriction or excessive size early on.

How Is This Test Performed?

This is not a blood or urine test. Instead, it’s measured using ultrasound imaging during a prenatal visit. Your provider will use special tools to estimate the circumference of your baby’s head based on their gestational age.

What Does the Result Mean?

The result helps your healthcare team assess whether your baby’s growth aligns with expected patterns for your stage in pregnancy. It doesn’t provide a single number but is part of a broader evaluation of fetal development.

What Are Common Reasons for Testing?

Fetal head circumference may be checked if you have risk factors for complications (like high blood pressure or diabetes), if your baby’s growth seems slower or faster than expected, or as part of routine prenatal care.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Fetal head circumference is a critical indicator of fetal well-being. While it doesn’t diagnose every condition on its own, it can signal potential concerns that may require further evaluation, such as intrauterine growth restriction or macrosomia (excessive fetal size). Regular monitoring helps ensure timely interventions if needed.

Short name

Fetal Head Circumference (GA)

Frequently asked questions

What does a fetal head circumference test involve?
This test uses ultrasound imaging to estimate the size of your baby’s head during a prenatal appointment. It’s a painless, non-invasive procedure that doesn’t require preparation beyond being comfortable for the ultrasound.
How often is fetal head circumference checked?
Frequency depends on your pregnancy and health status. It may be checked more often if you have risk factors or if your provider monitors fetal growth closely, or as part of routine visits during mid-to-late pregnancy.
Can abnormal results affect my pregnancy?
Abnormal results may prompt further testing or discussions with your provider to rule out or address potential concerns. However, many pregnancies proceed without issues, and results are always interpreted in the context of your overall health and fetal development.
  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