This is the ValueSet that contains all the codes in LOINC Codes (http://hl7.org/fhir/ValueSet/observation-codes) and Pregnancy Expected Delivery Date Method - IPS (http://hl7.org/fhir/uv/ips/ValueSet/edd-method-uv-ips). E.g. what you have to deal with if you get resources containing codes in either of them