Oestradiol implants for gender-affirming hormone therapy: an observational study of serum oestradiol levels and consumer survey.

Background: Custom-compounded subcutaneous implants are being used widely in Australia for gender-affirming hormone therapy. However, there is no published literature regarding their use for this purpose.

Methods: Electronic medical records were audited for consecutive clients who received oestradiol implants April 2019-November 2022 in gender clinics held within Hunter New England Health District in New South Wales, Australia. Serum oestradiol levels were analysed for implant doses 50-200mg, and predicted oestradiol level was modelled following 100mg implant insertion. An electronic consumer survey was sent to a convenience sample of implant recipients.

Results: A total of 38 clients received 88 implants, with 100mg oestradiol implants being the most frequently used (68%). The median interval between insertion procedures was 270 (IQR 186-399) days. The median serum oestradiol levels following implant insertion, for all implants combined, were within the target range of 250-600pmol/L at 1-, 3-, 6-, 9- and 12-month time points. Following insertion of a 100mg implant, the estimated time to reach a predicted serum oestradiol of ≤250pmol/L was 4months after an initial implant, and 13months after subsequent implants. Seventeen consumer surveys were received from 28 invitations. All respondents had previous experience of oral and/or transdermal oestradiol use. Oestradiol implants were preferred due to ease of use, perceived effectiveness, and the belief that other methods were less safe or associated with intolerance and side effects.

Conclusions: Oestradiol implants are effective in achieving target serum oestradiol levels over a sustained period. Further research with larger cohorts could identify the optimal dosage regimen.