A central theme that recurs throughout Detransition, Baby is the performative nature of gender. The concept of gender performativity is central to feminist and gender studies and is often associated with feminist theorist Judith Butler’s book Gender Trouble (1990). In the view of scholars like Butler, gender is a set activities and behaviors that individuals perform, and we learn to enact behaviors that follow societal codes for how a man or a woman should behave. According to this theory, gender is constructed and learned through social interactions, and is not an innate set of qualities that one is born with.

Throughout her novel, Peters explores how gender performativity impacts the lives of both Reese and Amy, who strive to perform femininity in such a way that they will pass as cisgender (that is, be perceived by others as people whose current genders match the ones they were assigned at birth). One of the main ways people perform gender is through physical appearance, including clothes, physical mannerisms, body adornment, and aesthetic choices. Reese and Amy both suffer from gender dysphoria—stress that occurs in trans individuals who feel a mismatch between their physical bodily appearance and their gender. For Reese, gender dysphoria arises from not having a vagina, as well as from her desire for a more feminine face shape.