Sperm-producing transgender individuals may want to have biological children in the future, using their sperm to fertilize either a partner’s egg or a donated egg. Sperm freezing makes this possible, and is recommended before undergoing gender-affirming hormone therapy (typically estrogen and androgen-blockers).
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 a few days and reduced sperm concentration after 2 weeks.
In some cases, sperm count and quality can be recovered. One study suggested that, within 6 months of stopping estrogen therapy, 67% of subjects returned to 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.
Sperm freezing prior to hormone therapy offers an option for trans women to preserve their ability to become a genetic parent, and to avoid the need for long-term cessation of their hormone treatment later on.
Historically, many trans people did not get adequate counseling on their fertility prior to starting hormone therapy. That seems to be changing. A study in 2018 analyzed sperm samples in a sperm bank, finding that the number of transgender sperm bankers increased by 18% relative to cisgender sperm bankers from 2006 to 2016.