A Mouse Model to Investigate the Impact of Gender Affirming Hormone Therapy with Estradiol on Reproduction

Fertility in transgender and gender diverse people: systematic review of the effects of gender-affirming hormones on reproductive organs and fertility

BACKGROUND

Transgender and gender diverse (TGD) people seek gender-affirming care at any age to manage gender identities or expressions that differ from their birth gender. Gender-affirming hormone treatment (GAHT) and gender-affirming surgery may alter reproductive function and/or anatomy, limiting future reproductive options to varying degrees, if individuals desire to either give birth or become a biological parent.

OBJECTIVE AND RATIONALE

TGD people increasingly pursue help for their reproductive questions, including fertility, fertility preservation, active desire for children, and future options. Their specific needs certainly require more insight into the effects of GAHT on gonads, gametes, and fertility. This systematic review aims to provide an overview of the current knowledge on the impact of GAHT on gonads, gametes, fertility, fertility preservation techniques, and outcomes.

SEARCH METHODS

This review was registered in the PROSPERO registry under number CRD42024516133. A literature search (in PubMed, Embase, and Web of Science) was performed with a medical information specialist until 15 November 2024.

OUTCOMES

In all TGD people using GAHT, histological changes have been reported.Using testosterone GAHT, ovarian cortical and stromal changes were reported by various studies. In most studies, persistent activity in folliculogenesis can be concluded based on the descriptions of the follicle count, distribution, and oocyte retrieval yield. However, there may be a negative effect on the fertilization rate in the presence of testosterone. Reports of successful ovarian stimulation, fertilization, pregnancies, and live births have been published, describing cases with and without testosterone discontinuation.After using oestrogen GAHT, testes are reported to be more atrophic, including smaller seminiferous tubules with heavy hyalinization and fibrosis. Spermatogenic levels varied widely from complete spermatogenesis to meiotic arrest with spermatids, to spermatogonial arrest, Sertoli cells only, or even tubular shadows. Oestrogen and anti-androgen treatment causes higher proportions of sperm abnormalities (i.e. low total sperm count, low sperm concentration, poor sperm motility) or azoospermia. However, after cessation, this may be restored.

WIDER IMPLICATIONS

Although knowledge of the effect of GAHT is growing, blind spots remain to be uncovered. Therefore, additional research in this specific population is needed, preferably comparing outcomes before and after the start of GAHT. This may help to reveal the pure impact of GAHT on reproductive functioning. Research suggestions also include investigations into the reversibility of the GAHT effect, especially for those who start transition at a young age. Looking carefully at the presented data on GAHT effects on gonads and gametes, the correct advice is to assess and reassess reproductive wishes and preferences repeatedly, and also to explore individual fertility preservation needs during gender-affirming treatment, given the expanding knowledge and therapy opportunities. Finally, concerns regarding long-term health outcomes and quality of life of children born by the use of gametes preserved after exposure to GAHT require prospective follow-up studies.

[Fertility preservation in persons with gender incongruence and male-assigned sex at birth]

According to current guidelines, patients with gender incongruence seeking treatment must receive appropriate education and counselling from healthcare professionals on the various options for fertility preservation. Gender-affirming hormonal treatment leads in persons assigned male at birth to a reduction of LH, FSH, and testosterone, which is associated with a regression of spermatogenesis (up to complete loss) and subsequent testicular atrophy. Individuals starting gender-affirming hormonal treatment after having experienced male puberty may provide an ejaculate sample for sperm cryopreservation. In cases where no sperm is detected in the ejaculate due to gender-affirming hormonal treatment, or if the sampling of ejaculate is no longer possible or causes excessive psychological distress, (microsurgical) testicular sperm extraction [(m)TESE] should be offered. Electroejaculation under anaesthesia is rarely effective, as hormonal treatment impairs spermatogenesis. Similarly, microsurgical epididymal sperm aspiration (MESA) is not typically effective for the same reason. If adolescents with gender incongruence undergo puberty blockade and/or gender-affirming hormonal treatment at an early stage of puberty (possible from Tanner stage 2), this prevents the maturation of spermatogonial stem cells into mature sperm. Puberty blockade with GnRH reduces the secretion of LH and FSH by the pituitary gland, which, in turn, suppresses the production of testosterone in the Leydig cells and the stimulation of spermatogenesis in the testicles. In such cases, the cryopreservation of spermatogonial stem cells is possible, similar to how it is offered in some countries for peri-pubertal patients prior to necessary germ cell-toxic treatments. In Germany, there is a relevant network (Androprotect), which was founded in Münster in 2012. Via Androprotect, this procedure is also offered for adolescent individuals with gender incongruence. This approach is considered experimental as no established treatment exists for the refertilisation of affected adults at a later stage, although several procedures for in-vitro sperm maturation and tissue transplantation are under development. The care of patients with gender incongruence should include individual counselling provided by experienced professionals in an interdisciplinary treatment team. Individual treatment approaches should be offered to facilitate shared decision-making (based on informed consent) to ensure that each individual can make an informed and appropriate decision regarding fertility preservation.

Male animal sterilization: history, current practices, and potential methods for replacing castration

Sterilization and castration have been synonyms for thousands of years. Making an animal sterile meant to render them incapable of producing offspring. Castration or the physical removal of the testes was discovered to be the most simple but reliable method for managing reproduction and sexual behavior in the male. Today, there continues to be global utilization of castration in domestic animals. More than six hundred million pigs are castrated every year, and surgical removal of testes in dogs and cats is a routine practice in veterinary medicine. However, modern biological research has extended the meaning of sterilization to include methods that spare testis removal and involve a variety of options, from chemical castration and immunocastration to various methods of vasectomy. This review begins with the history of sterilization, showing a direct link between its practice in man and animals. Then, it traces the evolution of concepts for inducing sterility, where research has overlapped with basic studies of reproductive hormones and the discovery of testicular toxicants, some of which serve as sterilizing agents in rodent pests. Finally, the most recent efforts to use the immune system and gene editing to block hormonal stimulation of testis function are discussed. As we respond to the crisis of animal overpopulation and strive for better animal welfare, these novel methods provide optimism for replacing surgical castration in some species.

A Review of Animal Models Investigating the Reproductive Effects of Gender-Affirming Hormone Therapy

Gender-affirming hormone therapy (GAHT) is an important component in the process of transitioning for many transgender and gender-diverse (TGD) individuals. Multiple medical organizations recommend fertility preservation counseling prior to initiation of GAHT; however, there remains little high-quality data regarding the impact of GAHT on fertility and reproductive function. A PubMed literature review was performed using Boolean search operators linking keywords or phrases such as "mouse", "rat", "primate", "animal model", "transgender", "gender", "estrogen", "testosterone", "fertility", and "fertility preservation". Recent research has produced a number of animal models of GAHT that utilize similar hormonal regimens and produce similar phenotypic results to those used and observed in human patients. Specific to testosterone(T)-containing GAHT, animals demonstrate loss of menstrual cyclicity with therapy, resumption of menses on cessation of therapy, suppression of gonadotropin levels, and physical changes such as clitoromegaly. Models mimicking GAHT for transmasculine individuals in the peripubertal period demonstrate that pretreatment with GnRHa therapy does not modify the effects of subsequent T administration, which were similar to those described in adult models. Both models suggest promising potential for future fertility with cessation of T. With estradiol (E)-containing GAHT, animals exhibit decreased size of testicles, epididymis, and seminal vesicles, as well as ongoing production of spermatocytes, and seminiferous tubule vacuolization. Given the ethical challenges of conducting human studies in this area, high-fidelity animal models represent a promising opportunity for investigation and could eventually transform clinical counseling about the necessity of fertility preservation. Future studies should better delineate the interactions (if any exist) between treatment attributes such as dosing and duration with the extent of reversibility of reproductive perturbations. The development of models of peripubertal feminizing GAHT is an additional area for future work.