This is the ValueSet that contains all the codes in LOINC Codes (http://hl7.org/fhir/ValueSet/observation-codes) and Cigarette Smoking Before and During Pregnancy (http://hl7.org/fhir/us/bfdr/ValueSet/cigarette-smoking-before-during-pregnancy). E.g. what you have to deal with if you get resources containing codes in either of them