http://hl7.org/fhir/us/core/StructureDefinition/us-core-head-circumference|8.0.0-ballot

The US Core Head Circumference Profile inherits from the US Core Vital Signs Profile. This profile sets minimum expectations for the Observation resource to record, search, and fetch head circumference observations with a standard LOINC code and UCUM units of measure. It specifies which *additional* core elements, extensions, vocabularies, and value sets **SHALL** be present in the resource and constrains how the elements are used. Providing the floor for standards development for specific use cases promotes interoperability and adoption.