This code system http://hl7.org/fhir/relationship defines the following codes:

CodeDisplayDefinition
1SelfThe patient is the subscriber (policy holder)
2SpouseThe patient is the spouse or equivalent of the subscriber (policy holder)
3ChildThe patient is the child of the subscriber (policy holder)
4Common Law SpouseThe patient is the common law spouse of the subscriber (policy holder)
5OtherThe patient has some other relationship, such as parent, to the subscriber (policy holder)