What does this LOINC code represent?

This LOINC code identifies a lab observation, measurement, question, or clinical concept in a standardized format.

Is this enough to understand my test result?

No. The code identifies the test or observation, but the interpretation depends on the actual result, reference range, and clinical context.

LOINCActiveObservation

LOINC Code 33111-6: Gestational age estimated from Head circumference derived on US by Chitty 1997 method

Name: LOINC Code 33111-6: Gestational age estimated from Head circumference derived on US by Chitty 1997 method
Creator: HealthAssure Clinical Team
Published: 2026-05-21T08:59:20.066Z

33111-6 is a LOINC code used to identify Gestational age estimated from Head circumference derived on US by Chitty 1997 method in laboratory and clinical observation data. You may see this code in lab systems, lab reports, EHR exports, interoperability feeds, or other structured clinical data exchanges. LOINC codes identify tests, measurements, observations, survey items, and clinical questions in a standardized way. It is associated with the component Gestational age. It is commonly used with the system or sample type ^Fetus.

Reviewed by HealthAssure Clinical TeamUpdated 21 May 2026

What is this code?

LOINC codes identify tests, measurements, observations, survey items, and clinical questions in a standardized way. It is associated with the component Gestational age. It is commonly used with the system or sample type ^Fetus.

When is it used?

Used in lab systems, EHRs, and clinical data exchange.
May identify a test, observation, survey item, or clinical document request rather than a diagnosis.
Status: ACTIVE
Order vs observation: Observation
Method: US+Estimated from HC derived.Chitty 1997

What it does not mean

The code identifies the observation or test, not the actual result.

Key facts

Gestational age estimated from Head circumference derived on US by Chitty 1997 method
Gestational age
97; Echography; Est; estimation; Fetal; GA; Gest; Gestation; Gyn; Gynecology; Head Circumference; OB; ObGyn; OBSTERICAL; OBSTERICAL.ULTRASOUND; Obstetrical; Obstetrics; Point in time; predicted; Prenatal; QNT; Quan; Quant; Quantitative; Random; Sonogram; Sonograph; Sonography; ULS; Ultrasound

Where you may see this code

You may see this code in lab systems, lab reports, EHR exports, interoperability feeds, or other structured clinical data exchanges.

Common synonyms

Gestational age estimated from Head circumference derived on US by Chitty 1997 methodGA from HC derived.Chitty 1997Gestational ageOB.USTimePt^Fetus

Frequently asked questions

Code details

Code33111-6

SystemLOINC

Display nameGestational age estimated from Head circumference derived on US by Chitty 1997 method

DescriptionGestational age

Short nameGA from HC derived.Chitty 1997

ComponentGestational age

PropertyTime

TimingPt

System (specimen)^Fetus

ScaleQn

MethodUS+Estimated from HC derived.Chitty 1997

ClassOB.US

Example unitsdays

StatusACTIVE

Order/ObservationObservation

Flags

BillableNo

Valid clinical useNo

Source

SourceLOINC

Version2.82

Releasemain

First released2.09

Last changed2.70

Part names

Gestational ageTimePt^FetusQnUS+Estimated from HC derived.Chitty 1997Time (e.g. seconds)Point in time (spot)Ultrasound+Estimated from HC Derived.Chitty 1997

About this content

This page is prepared by HealthAssure's clinical team using official coding standards from LOINC. AI tools assist with drafting explanations, which are then reviewed and verified by healthcare professionals for accuracy. This content is for informational purposes and does not replace professional medical advice. Meet our team.