People in the Fifth World do not generally consider gender a binary, nor do they consider it interchangeable with biological sex.
The most conservative societies recognize only two genders, which usually - but not always - line up with biological sex. Members of these societies may choose their preferred gender upon reaching adulthood.
Most societies, however, recognize around three to five genders, each with its own expected role. Consistent with their egalitarianism, Fifth Worlders do not elevate one gender above any others. All genders have vital roles to play in a family.