Could you add an option for genders other than male or female? The easiest would be to have it a field that the person can fill however they want, but if you're going to add other options, I would suggest trans male, trans female, genderqueer and "other". It would probably be nice as well for the male and female to be changed to cis male and cis female to match.
If you only add one, it's usually a good rule for that one to be "other" so that whoever doesn't fit in the rest has something that matches them.
Haven't played with it much yet, I might give you more feedback after I do.