The Role of Estrone in Feminizing Hormone Treatment

In trans women, hormone treatment induces feminization; however, the degree of feminization varies from person to person. A possible contributing factor could be estrone, a weak estrogen that interferes with the estrogen receptor.

We assessed whether estrone is involved in feminization induced by hormone treatment.

This prospective cohort study, with follow-up of 1 year, included 212 adult trans women at a gender identity clinic, who were starting gender-affirming hormone treatment between July 2017 and December 2019, median age 25 years. Change in fat percentage and breast development were assessed.

After 12 months of hormone treatment, estrone concentration was 187 pmol/L (95% CI, 153-220) in transdermal and 1516 pmol/L (95% CI, 1284-1748) in oral estradiol users. Fat percentage increased by 1.2% (interquartile range [IQR], 0.3-4.8) in transdermal and 4.6% (IQR, 2.5-5.9) in oral estradiol users. This was not associated with estrone concentrations in transdermal (+4.4% (95% CI, -4.0 to 13) per 100 pmol/L increase in estrone concentration) nor in oral estradiol users (-0.7% [95% CI, -1.7 to 0.3]). Breast volume increased by 69 mL (IQR, 58-134) in transdermal and 62 mL (IQR, 32-95) in oral estradiol users. This was not associated with estrone concentrations in transdermal (+14% [95% CI, -49 to 156] per 100 pmol/L increase in estrone concentration) nor oral estradiol users (+11% [95% CI -14 to 43]).

Change in fat percentage and breast development in trans women were not associated with estrone concentrations nor with administration route. Therefore, measurement of estrone concentrations does not have a place in the monitoring of feminization in trans women.