Aim, design and setting of the study
In order to determine the effects and side effects of adding oral progesterone to feminizing GAHT, we set up a non-blinded, non-placebo, randomized controlled trial, using a 2 × 3 factorial design. This study design allows for rapid assessment of potential effects of progesterone treatment and dose combinations on breast volume and may serve as a pilot project for a larger study in transgender women at the start of hormone treatment before surgery. This is a mono-center study at the Center of Expertise on Gender Dysphoria of Amsterdam UMC, location VUmc, a national referral center for individuals experiencing gender incongruence.