The standard_concept_id for birthweight is 4264825, which goes into the Domain MEASUREMENT, Class Observable Entity. SNOMED Vocabulary. However the standard_concept_id for pregnancy weight gain is 40759199, which goes into the Domain OBSERVATION, Class Clinical Observation, LOINC Vocabulary. Why is Pregnancy weight gain an OBSERVATION rather than a MEASUREMENT concept?
Despite the short name of the LOINC concept, “Weight gain [Mass] --during current pregnancy,” which may look like a measurement taken during a clinical visit, this concept actually originated as a survey question. Its full text is “How much weight have you gained during this pregnancy?”
Therefore, the value represents self-reported information collected through a questionnaire, rather than a measurement performed during a clinical encounter. This is why the concept belongs to the Observation domain.
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