in cbc:GenderCode description there is a reference to the ISO 5218 code list .. that only contains these options:

• 0 = Not known;
• 1 = Male;
• 2 = Female;
• 9 = Not applicable.

Given the sensitivity of Gender I would propose to remove that reference  .. so people would feel more comfortable using code lists that would also allow other genders then those defined in the ISO code list.