At Register Now, we are big advocates of inclusiveness in the world of sporting events. With that in mind, a third gender option is possible within your registration flow. 

If you have Gender switched on in your Participant Fields, you will now see the option to 'Show Not Specified' in your registration flow (similar to all our participant fields, you do have the option to have this on or off):

If this is enabled, a 3rd option will now show for gender as your participants move through your form: