Facebook announced that it has expanded gender identity options again. Now users in a limited number of countries will be able to fill in a free-form field, if their gender identity doesn't align with any of the current options offered by Facebook. In February of 2014, Facebook expanded some of the options on profiles to include 51 gender options.
From Facebook: "We recognize that some people face challenges sharing their true gender identity with others, and this setting gives people the ability to express themselves in an authentic way." The expanded custom gender field is available to users in 10 countries, including the United States.
The expanded gender options correspond with the ability to use preferred pronouns and adjust privacy settings for gender.