Male or Female
Spouse means a husband or wife, considered in relation to their partner. So, spouse is a common gender.
There are 4 types of gender. Masculine, Feminine, Neuter and Common. "Spouse" doesn't means only male or only female, it cannot be Masculine or Feminine gender. So, Neuter and Common gender are left.
What is neuter gender? Neuter gender refers to a grammatical category of words which are neither masculine nor feminine. But, "Spouse" means both husband and wife. That's why it is a common gender.