Hormone therapy changes the fertility preservation conversation for trans and gender-diverse patients

For anyone starting gender-affirming hormone treatment (GAHT), fertility is rarely the first thing on their mind. This is understandable given their age, as the priority is usually to begin feeling more like themselves as quickly as possible. But for those who might want to have a genetically related child one day, the timing of that decision can matter more than many people realise.

New data from our unit at Guy's and St Thomas' NHS Foundation Trust in London, and presented at the 42nd Annual Meeting of the European Society of Human Reproduction and Embryology (ESHRE) in London last month, suggest it matters in different ways depending on a person's reproductive anatomy.

We work in the Fertility Preservation Service at Guy's Hospital, where over the past few years we have run the TransFertility project: a dedicated pathway for transgender and gender-diverse patients who want to freeze their gametes before, or even after, their medical transition.

Guidance from international bodies such as ESHRE has long recommended that fertility options be discussed before hormone treatment begins. Until now, counselling has largely relied on expert opinion because clinicians had little evidence about how the timing of GAHT affects fertility preservation success. What has been less clear, until now, is exactly how much of a difference timing actually makes, and whether that difference looks the same for everyone.

To find out, we looked back at four years of our own referral data. We reviewed 158 people referred to our service, split between those with testes and those with ovaries, because the two groups face quite different biological realities and therefore need different conversations. We compared outcomes for patients who had already started GAHT by the time they came to us with those who had not.

For people with testes, comprising mostly transfeminine patients on oestrogen, sometimes combined with anti-androgen medication, the difference was striking. Among those already on GAHT, 30 percent had a failed sperm freezing attempt the first time they tried, compared with fewer than four percent of those who had not yet started treatment. This is consistent with what is already known, since GAHT leads to profound suppression of spermatogenesis.

Importantly, fertility suppression was not always permanent. Nearly all patients (except one) who initially failed sperm cryopreservation were able to bank sperm successfully after stopping GAHT for three to six months, consistent with the duration of spermatogenesis.

The picture for people with ovaries, corresponding largely to transmasculine patients on testosterone, was considerably more reassuring. Testosterone does not reliably stop periods and ovulation, and for fertility preservation purposes, the number of mature eggs suitable for freezing was essentially the same whether or not someone had been on GAHT.

There was a hint that longer exposure to testosterone might modestly reduce the number of eggs collected, but this trend did not reach statistical significance and could equally reflect long-standing suppression rather than a genuine biological effect. Larger, longer-term studies would be needed to know whether it is real.

Why the difference between the two groups? Sperm production is a continuous, ongoing process that GAHT can suppress quickly, producing something close to an all-or-nothing effect. Testosterone's effect on the ovaries, by contrast, is more variable, but it does not appear to meaningfully deplete the store of eggs already present, at least not over the timeframes we were able to study.

What does this mean in practice? For people with testes, our findings support what many fertility specialists already suspected but could not always quantify: that banking sperm before starting hormone treatment, or very early into it, meaningfully improves the odds of successful storage.

For people with ovaries, the picture opens up a genuinely useful piece of flexibility. The implications extend beyond biology. Because GAHT exposure does not appear to reduce egg numbers substantially, there may be room to postpone fertility preservation to a later point in life rather than feeling compelled to preserve fertility before starting testosterone. This matters both biologically and practically. Egg quality is generally highest in the twenties before the age-related decline begins, while ovarian reserve remains favourable for most individuals during this period.

It also matters for funding. NHS support for gamete storage is usually time-limited, covering only a set number of years depending on the Integrated Care Board that a patient's GP surgery falls within, so preserving fertility too early can mean that funded storage runs out before someone is actually ready to use it. Timing preservation a little later, when biology is at its most favourable and the funded storage window lines up more closely with a person's likely reproductive years, could make NHS support stretch further and serve patients better.

It is worth being clear about the limitation of this work. It comes from a single centre, the numbers were analysed retrospectively, and although they are among the largest reported for this population, they remain modest. We could not fully account for every factor that might affect results. We also do not yet know whether eggs collected after testosterone exposure go on to produce healthy pregnancies – ultimately the outcome that matters most to patients. We would therefore describe these findings as informative rather than final, offering a solid basis for counselling patients honestly about probabilities, not a guarantee of what will happen for any individual.

This study grew directly out of the TransFertility pathway itself, which we built because a formalised, welcoming, rapid access route into fertility preservation simply did not exist for transgender and gender-diverse patients in most of the NHS. We have described that service model, along with a wider review of the evidence in this area, in a separate paper in Reproductive BioMedicine Online.

Since launching in November 2022, referrals into the service have increased more than nineteen-fold, and the vast majority of patients who start treatment go on to complete it. We think this reflects something simple: when a pathway is designed around the people it serves, more of them are able to use it.

One of the biggest takeaways from this work has been the need for a clearly defined referral pathway for this patient cohort. The implementation of clear administrative pathways can make a world of difference for transgender patients waiting to commence GAHT.

The wider lesson from the TransFertility project is not simply that fertility preservation should be offered. It is that patients need access to timely, evidence-based counselling before irreversible decisions are made. Our findings suggest that this counselling should not be the same for everyone. For people with testes, delaying sperm banking may substantially reduce the chance of successful cryopreservation. For people with ovaries, the evidence is more reassuring, allowing greater flexibility in timing and potentially making better use of both biology and NHS resources.

As the number of transgender and gender-diverse people seeking GAHT continues to rise, providing nuanced rather than uniform fertility advice will become an increasingly important part of high-quality reproductive healthcare.