Aims: Subdermal oestradiol implants can be used in place of tablets, gels, and patches for feminising gender affirming hormone treatment (GAHT). Pellet use is increasingly preferred by patients. However, studies of oestradiol pellet use in gender diverse individuals are lacking.

Methods: We report cross sectional oestradiol concentration data in a cohort of gender diverse individuals undergoing GAHT with subdermal oestradiol pellets. For all individuals, two 100mg pellets were inserted at baseline, and their previous oestradiol treatment was ceased. Approximately 6-months after the initial implant insertion, a single 100mg pellet was inserted irrespective of oestradiol level. Subsequent 100mg pellets were then inserted based on serum oestradiol concentrations, at intervals of approximately 12-months.  

Results: 70 individuals underwent at least two implant procedures and had oestradiol concentrations available for assessment. The median age was 26 years (range 17-51), with most transitioning to implants from oral oestradiol tablets.

In 70 individuals, a second implant was inserted a median 6-months after the initial procedure, with a median pre-implant oestradiol concentration of 391 (178-749) pmol/L.

In 35 individuals, a third implant was inserted at a median 17-months, with median pre-implant serum oestradiol concentration of 451 (241-964) pmol/L.

In 18 individuals, a fourth implant was inserted at a median 30-months, with median pre-implant oestradiol concentration of 446 (334-722) pmol/L.

Nine individuals had a fifth implant insertion (median 38-months) and 3 individuals underwent a sixth and seventh implant at a median 42- and 55-months respectively. Median oestradiol concentration prior to the fifth, sixth, and seventh implants were 508, 545, and 505 (range 295-689) pmol/L (Figure 1).

Conclusion: The use of subdermal oestradiol pellets for GAHT results in predictable serum oestradiol levels over time. Using our treatment protocol, supratherapeutic and subtherapeutic oestradiol concentrations were rare, even during long term use out to 4-years.