NCPI FHIR Implementation Guide v2
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: Biological Relationship Codes - XML Representation

Draft as of 2025-12-03

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<ValueSet xmlns="http://hl7.org/fhir">
  <id value="family-biological-relationship-vs"/>
  <text>
    <status value="extensions"/>
    <div xmlns="http://www.w3.org/1999/xhtml"><p class="res-header-id"><b>Generated Narrative: ValueSet family-biological-relationship-vs</b></p><a name="family-biological-relationship-vs"> </a><a name="hcfamily-biological-relationship-vs"> </a><p>This value set includes codes based on the following rules:</p><ul><li>Include these codes as defined in <a href="http://terminology.hl7.org/6.2.0/CodeSystem-v3-nciThesaurus.html"><code>http://ncicb.nci.nih.gov/xml/owl/EVS/Thesaurus.owl</code></a><span title="Version is explicitly stated to be 3.0.0"> version &#x1F4CD;</span><table class="none"><tr><td style="white-space:nowrap"><b>Code</b></td><td><b>Display</b></td></tr><tr><td>C96580</td><td>Biological Mother</td></tr><tr><td>C96572</td><td>Biological Father</td></tr></table></li><li>Include these codes as defined in <a href="http://terminology.hl7.org/7.0.0/CodeSystem-v3-RoleCode.html"><code>http://terminology.hl7.org/CodeSystem/v3-RoleCode</code></a><span title="Version is explicitly stated to be 3.0.0"> version &#x1F4CD;3.0.0</span><table class="none"><tr><td style="white-space:nowrap"><b>Code</b></td><td><b>Display</b></td><td><b>Definition</b></td></tr><tr><td><a href="http://terminology.hl7.org/7.0.0/CodeSystem-v3-RoleCode.html#v3-RoleCode-ITWIN">ITWIN</a></td><td>identical twin</td><td>The scoper and player are offspring of the same egg-sperm pair.</td></tr></table></li></ul></div>
  </text>
  <url
       value="https://nih-ncpi.github.io/ncpi-fhir-ig-2/ValueSet/family-biological-relationship-vs"/>
  <version value="0.2.0"/>
  <name value="FamilyBiologicalRelationshipVS"/>
  <title value="Biological Relationship Codes"/>
  <status value="draft"/>
  <experimental value="false"/>
  <date value="2025-12-03T22:26:51+00:00"/>
  <publisher value="NCPI FHIR Working Group"/>
  <contact>
    <name value="NCPI FHIR Working Group"/>
    <telecom>
      <system value="url"/>
      <value value="https://www.ncpi-acc.org/about/working-groups"/>
    </telecom>
    <telecom>
      <system value="email"/>
      <value value="ncpi-fhir-ig@googlegroups.com"/>
    </telecom>
  </contact>
  <description
               value="List of codes indicating the biological relationship between two individuals
in a family. It is restrictive to encourage a standardized representation.

# Code Selection Rationale

## Parent Codes

We use the NCI Thesaurus here for the mother and father because its
definitions are more precise.

- [`C96572` (**&quot;Biological Father&quot;**)](https://evsexplore.semantics.cancer.gov/evsexplore/concept/ncit/C96572):
   A male who contributes to the genetic makeup of his offspring through
   the fertilization of an ovum by his sperm.
- [`C96580` (**&quot;Biological Mother&quot;**)](https://evsexplore.semantics.cancer.gov/evsexplore/concept/ncit/C96580):
   A female who contributes to the genetic makeup of her offspring
   from the fertilization of her ovum.

In contrast, the parental family-role's codes are less refined:

- [`NMTH` (**&quot;natural mother&quot;**)](https://terminology.hl7.org/6.5.0/CodeSystem-v3-RoleCode.html#v3-RoleCode-NMTH):
   The player of the role is a female who conceives
   or gives birth to the scoping entity (child).
- [`NFTH` (**&quot;natural father&quot;**)](https://terminology.hl7.org/6.5.0/CodeSystem-v3-RoleCode.html#v3-RoleCode-NFTH):
   The player of the role is a male who begets the
   scoping entity (child).

In particular, **&quot;Biological Mother&quot;** excludes surrogates but
`NMTH` is ambiguous. **&quot;Biological Father&quot;** specifies
fertilization of an ovum by sperm, whereas `NFTH` uses the
ambiguous term &quot;begets,&quot; which could include other
mechanisms.

## Twin Codes

For twins, we use the RoleCode `ITWIN` code rather than the NCI `C73429`.

- [`C73429` (**&quot;Identical Twin&quot;**)](https://evsexplore.semantics.cancer.gov/evsexplore/concept/ncit/C73429):
   Either of the two offspring resulting from a shared ovum.
- [`ITWIN` (**&quot;Identical Twin&quot;**)](https://terminology.hl7.org/6.5.0/CodeSystem-v3-RoleCode.html#v3-RoleCode-ITWIN):
   The scoper and player are offspring of the same egg-sperm
   pair.

Though being &quot;offspring&quot; of the same fertilized egg is
questionable wording, we use `ITWIN` because it also allows
other multiples (triplets, quadruplets, etc.) to be
represented with the same code whereas `C73429` is only for
twins.

# Note for upgrading to FHIR R5

When we add support for R5 to the IG, we should add the rest of the
codes from &lt;http://terminology.hl7.org/ValueSet/v3-FamilyMember&gt;
as additional bindings to guide users when not using one of the
main bindings.

We intend that when users need to use a code that is not in
the main bindings, they should default to the FamilyMember
ValueSet. However, in R4, there is no way to express this
in the ValueSet itself."/>
  <compose>
    <include>
      <system value="http://ncicb.nci.nih.gov/xml/owl/EVS/Thesaurus.owl"/>
      <version value="3.0.0"/>
      <concept>
        <code value="C96580"/>
        <display value="Biological Mother"/>
      </concept>
      <concept>
        <code value="C96572"/>
        <display value="Biological Father"/>
      </concept>
    </include>
    <include>
      <system value="http://terminology.hl7.org/CodeSystem/v3-RoleCode"/>
      <version value="3.0.0"/>
      <concept>
        <code value="ITWIN"/>
        <display value="identical twin"/>
      </concept>
    </include>
  </compose>
</ValueSet>