(Comment about http://hl7.org/fhir/R4/observation-vitalsigns.html#vitals-table)
If these two codes mean the same thing, one should be sufficient. I'm not sure they do, though. Lying should be a option, not an addition
8306-3 -Body height - lying (i.e., body length - typically used for infants) MAY be included as an additional observation code.
(Comment 3 - imported by: Jean Duteau)