Testosterone is essential to the production of sperm. It plays a role in initiating several key processes in spermatogenesis, including the division and maturation of sperm cells. The goal of hormone therapy for transgender women is to decrease testosterone and increase estrogen levels to create a more typically feminine appearance. Estrogen therapy helps decrease testosterone levels in the body. Many trans women also use anti-androgens to further decrease their testosterone to typical female levels (around 70 ng/ml).
Testosterone levels under 264 ng/ml are associated with poorer semen parameters. And, as we would expect, use of estrogen and androgen-blockers is associated in research with poor sperm quality and lower sperm count. A 2017 review looked at nearly 40 years of research on the impact of cross-sex hormones on the sperm quality and testicular function of trans women. The review found that, in the majority of cases, estrogen and/or anti-androgen treatment caused reduced or halted spermatogenesis, as well as physical changes to the testicles.
The effect seems to be dose-dependent. In one study, a low-dose estrogen therapy had no impact on sperm concentration or motility, while a higher-dose regimen resulted in reduced sperm motility after just a few days and reduced sperm concentration after 2 weeks. Fertility preservation, including proactive sperm freezing, can help mitigate this.
Is infertility caused by gender-affirming hormones reversible?
In some cases, it appears to be. One study suggested that, within 6 months of stopping estrogen therapy, 67% of subjects recovered a normal sperm count.
However, the impact of medical gender transition on fertility, as well as the capacity for spermatogenesis to recover if estrogen treatment is paused, seem to be variable and individual. Case studies demonstrate that, while some patients continued spermatogenesis through gender-affirming hormone treatment, others stopped producing sperm altogether, and several experienced azoospermia for 4–5 months after pausing therapy.