Key takeaways:
- Exogenous testosterone suppresses the pituitary signals that drive sperm production, and a 2018 Endocrine Society guideline recommends against starting testosterone therapy in men who plan to have children in the near term (Bhasin et al., Journal of Clinical Endocrinology & Metabolism, 2018).
- Testosterone prescriptions among reproductive age men in the United States roughly quadrupled between 2003 and 2013, rising from 29.2 to 118.1 users per 10,000 person years (Rao et al., Journal of Urology, 2017), so this is not a rare decision men are being asked to make.
- A baseline semen analysis and hormone panel, taken before the first dose, is the only way to later tell whether a fertility problem was already there or was caused by the treatment.
A lot of men start testosterone therapy the same way they'd start any other prescription: symptoms first, paperwork second, and a follow up blood draw in a few months to see if the number moved. For low energy, low libido, or trouble building muscle, that approach is mostly harmless. For fertility, it is not, because testosterone therapy is one of the few common prescriptions that can shut down sperm production almost entirely, and by the time a man notices, there is no longer a clean baseline to compare against.
This article is about the testing that should happen before that first injection, gel, or pellet, not after. It is not a case against testosterone therapy. Plenty of men need it and benefit from it. It is a case for knowing exactly where your fertility stands before you start something that can change it, and for understanding why the medical guidelines already say this, even though it does not always happen in practice.
What does testosterone replacement therapy actually do to sperm production?
Testosterone replacement therapy suppresses natural sperm production because the body's hormonal control system cannot tell the difference between testosterone made by the testes and testosterone injected or applied from outside. Sperm production depends on a signaling chain called the HPG axis: the hypothalamus releases GnRH, which tells the pituitary gland to release LH and FSH, which tell the testes to produce testosterone and support developing sperm. When testosterone arrives from an outside source instead, the brain detects a normal or high level circulating in the blood and reads that as a sign to slow down. GnRH pulses drop, LH and FSH fall, and the testes stop being told to do anything.
The part that catches most men off guard is that the testosterone level that matters for sperm production is not the one measured on a blood test. Intratesticular testosterone, the concentration inside the testes themselves, normally runs 50 to 100 times higher than the level in the bloodstream, and it is that local concentration, not the circulating one, that Sertoli cells need to support sperm as it develops. External testosterone can push a blood test number up into a healthy or even high range while the concentration inside the testes collapses, because the pituitary has stopped sending the LH signal that keeps local production going. A recent review of the mechanism describes this collapse in intratesticular testosterone, driven by suppressed LH and FSH, as the direct cause of the drop in sperm counts seen with both prescribed testosterone therapy and anabolic steroid use (Desai et al., Therapeutic Advances in Urology, 2022). Our deep dive on testosterone and fertility covers this mechanism, and what a testosterone result alongside FSH and LH actually tells you, in more depth.
What should you actually test before starting TRT?
Two things, ideally in the same visit or the same week, before the first dose: a semen analysis and a hormone panel.
The semen analysis should include concentration, progressive motility, and morphology, measured against WHO 6th Edition reference thresholds of at least 16 million sperm per milliliter, at least 32% progressive motility, and at least 4% normal morphology by strict Kruger criteria (Boitrelle et al., Life, 2021). Combining volume, concentration, and motility into a single total motile sperm count, or TMSC, is particularly useful here, since TMSC is also the number that later determines whether natural conception, IUI, or IVF with ICSI is realistic if fertility treatment becomes necessary. Our explainer on TMSC walks through how that threshold works. If this baseline is skipped and a man's count is already low before treatment for reasons unrelated to testosterone, such as varicocele or a prior injury, there is no way to later separate that preexisting problem from anything testosterone therapy adds on top of it. SwimScore measures concentration, motility, and morphology against these same WHO 6th Edition thresholds, alongside DNA fragmentation and the full hormone panel described below, in a single CLIA-certified process, which is the kind of one-time baseline this decision calls for.
The hormone panel should include total and free testosterone, LH, and FSH. This is the combination that tells a clinician what kind of low testosterone is actually present. Low testosterone with high LH and FSH points to a testicular problem, the testes cannot respond even when maximally signaled. Low testosterone with low or normal LH and FSH points to a pituitary or hypothalamic signaling problem, which is often more responsive to therapies that stimulate the body's own production rather than replace it. That distinction changes which treatment path preserves fertility and which one does not. The Endocrine Society's clinical practice guideline recommends confirming low testosterone with a reliable morning total testosterone measurement as the starting diagnostic step, and explicitly recommends against starting testosterone therapy in men who are planning to conceive in the near term (Bhasin et al., Journal of Clinical Endocrinology & Metabolism, 2018). Our FSH and LH articles explain how to read each of these results on their own.
What do the guidelines actually recommend, and does that match what happens in practice?
The guidance itself is fairly clear. The Endocrine Society's 2018 guideline calls for shared decision making before starting testosterone therapy, meaning a clinician should discuss the potential benefits and risks, including the effect on fertility, before writing the prescription, and it recommends against testosterone therapy specifically in men planning fertility in the near term (Bhasin et al., Journal of Clinical Endocrinology & Metabolism, 2018). For men who want to preserve the option of having children later while still addressing low testosterone symptoms now, the same body of guidance points toward alternatives that stimulate the body's own hormone production instead of replacing it, such as human chorionic gonadotropin, clomiphene, or enclomiphene, each of which keeps the LH and FSH signal active rather than shutting it off. Our explainer on enclomiphene as a fertility preserving alternative to TRT covers how that option works and who it fits, including the fact that it remains an off-label use, not an FDA-approved indication for male infertility.
Where this gets less reassuring is in how consistently that guidance is actually followed. In a 2010 survey of practicing American Urological Association members, 25% of urologists said they would still treat a man's idiopathic infertility with exogenous testosterone, a treatment that suppresses sperm production, while he and his partner were actively trying to conceive (Ko et al., Journal of Urology, 2012). A follow up survey of the same association's members found the number essentially unchanged eight years later, at 24.4% (Thaker et al., F&S Reports, 2020). These are trained specialists, and roughly a quarter of them reported they would still make this choice. That is not a reason to distrust your own doctor specifically, but it is a real reason not to assume the fertility conversation will automatically happen before a prescription does, especially outside a urology or reproductive medicine setting. Asking for a baseline semen analysis and hormone panel yourself, before you start, closes that gap regardless of whether the conversation comes up unprompted.
Who should prioritize this workup?
This matters most for men who have not finished building their family and are being offered testosterone therapy for classic low-T symptoms: low energy, reduced libido, difficulty with muscle mass, or a lab result flagged as borderline low. It also matters for men already using testosterone for performance or aesthetic reasons who are now thinking about starting a family, since the same suppression applies regardless of why the testosterone was started. The urgency is highest for anyone in this position who has not yet had children and does not want to close that door by default. It is also worth doing if you are choosing between TRT and enclomiphene, clomiphene, or hCG, since the FSH and LH pattern from your baseline panel is exactly what determines which of those alternatives makes physiological sense for you.
This is less urgent for men who have completed their families and are not planning more children, or for men who have already had a vasectomy and do not intend to reverse it. Testosterone therapy still carries other considerations for those men, but the fertility-specific testing described here is aimed at preserving an option they have already decided not to use.
What if you are already on TRT?
Baseline testing is most useful before starting, but it is not useless after. If you are already on testosterone therapy and thinking about having children, a current semen analysis and TMSC still tell you where things stand right now, and a hormone panel including FSH and LH will typically show the suppressed pattern directly, which confirms what is happening rather than leaving it as a guess. Recovery after stopping exogenous testosterone is possible for most men but takes time and depends on how long you were on it. Our testosterone and fertility article walks through the recovery timelines and the hCG and clomiphene based protocols clinicians use to speed that process along, generally over a minimum of about 12 weeks, which is roughly how long a full cycle of sperm development takes to complete.
What we are more skeptical about
It would be easy to overstate this into a rule that every man on testosterone therapy needs a full fertility workup regardless of his situation, and we do not think that is right. For a man in his sixties who is done having children and has no interest in reversing a vasectomy, a baseline semen analysis before starting TRT for low energy is not a meaningful use of anyone's time. We are also careful about the strength of the causal claim here. No trial has directly shown that getting a baseline semen analysis and hormone panel before TRT improves anyone's eventual chance of a pregnancy. What the evidence actually supports is narrower and still useful: testosterone therapy demonstrably suppresses the hormonal signals that drive sperm production, guideline bodies recommend testing and discussing fertility before starting it, and that discussion is inconsistently happening in real clinical practice. Testing beforehand does not guarantee a good outcome. It guarantees that you and your doctor are working from real numbers instead of assumptions, which is a more modest claim, and a true one.
Our take
We know that testosterone therapy suppresses the intratesticular testosterone concentration that spermatogenesis depends on, and that this is not a rare side effect but the direct, expected mechanism of the treatment. We know that guideline bodies recommend testing and a fertility conversation before starting it, particularly for men who have not finished having children. We also know, from surveys of urologists themselves, that this conversation and this testing do not happen as consistently as the guidelines assume, which means the responsibility for asking often falls on the patient.
What we do not know, and will not claim, is that a baseline workup by itself changes anyone's odds of eventually having a child. What it changes is something more immediate and still valuable: whether you and your doctor can tell, six months or two years from now, whether a fertility problem was there from the start or showed up after treatment began. Given how common testosterone prescriptions have become among men in their twenties, thirties, and forties, that is worth ten minutes and a semen cup before the first dose, not after.
FAQ
Does testosterone replacement therapy cause infertility?
It can. Exogenous testosterone suppresses LH and FSH, which collapses the intratesticular testosterone concentration that sperm production depends on, and this suppression is the expected mechanism of the treatment rather than a rare side effect (Desai et al., Therapeutic Advances in Urology, 2022).
What tests should I get before starting TRT if I want kids later?
A semen analysis with total motile sperm count, and a hormone panel covering total and free testosterone, LH, and FSH, both done before the first dose, so there is a real baseline to compare against later.
Can I take testosterone and still have kids?
Guidelines recommend against starting testosterone therapy in men planning to conceive in the near term, and instead point toward alternatives like hCG, clomiphene, or enclomiphene that raise testosterone by stimulating the body's own signaling rather than replacing it (Bhasin et al., Journal of Clinical Endocrinology & Metabolism, 2018).
Will my doctor bring up fertility before prescribing testosterone?
Not reliably. In surveys of American Urological Association members, roughly a quarter of urologists said they would still use testosterone to treat a man's infertility while he was actively trying to conceive, a rate that was unchanged across two surveys eight years apart (Ko et al., Journal of Urology, 2012; Thaker et al., F&S Reports, 2020).
Is it too late to test if I already started TRT?
No. A current semen analysis and hormone panel still show where things stand now, and can guide a recovery plan if you decide to stop, though recovery takes time and generally requires waiting at least 12 weeks to see a meaningful change.
References
- Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism. 2018;103(5):1715-1744. https://doi.org/10.1210/jc.2018-00229
- Desai A, Yassin M, Cayetano A, et al. Understanding and managing the suppression of spermatogenesis caused by testosterone replacement therapy (TRT) and anabolic-androgenic steroids (AAS). Therapeutic Advances in Urology. 2022;14:17562872221105017. https://pmc.ncbi.nlm.nih.gov/articles/PMC9243576/
- Ko EY, Siddiqi K, Brannigan RE, Sabanegh ES Jr. Empirical medical therapy for idiopathic male infertility: a survey of the American Urological Association. Journal of Urology. 2012;187(3):973-978. https://pubmed.ncbi.nlm.nih.gov/22264467/
- Thaker H, Ko EY, Sabanegh ES, Brannigan RE, Alukal JP, Samplaski MK. Empirical medical therapy for idiopathic male infertility. F&S Reports. 2020;1(1):15-20. https://pmc.ncbi.nlm.nih.gov/articles/PMC8244321/
- Rao PK, Boulet SL, Mehta A, et al. Trends in Testosterone Replacement Therapy Use from 2003 to 2013 among Reproductive-Age Men in the United States. Journal of Urology. 2017;197(4):1121-1126. https://pmc.ncbi.nlm.nih.gov/articles/PMC11056957/
- Boitrelle F, Shah R, Saleh R, et al. The Sixth Edition of the WHO Manual for Human Semen Analysis: A Critical Review and SWOT Analysis. Life. 2021;11(12):1368. https://pmc.ncbi.nlm.nih.gov/articles/PMC8706130/
Thinking about starting testosterone therapy and want a real baseline first? SwimScore Complete measures concentration, motility, morphology, DNA fragmentation, and a full hormone panel together from home, processed in the same CLIA-certified labs used by fertility clinics, so you have real numbers before you start.
Fertility clinics and urology practices: if patients are asking about TRT and fertility in the same visit, see how SwimScore can provide a complete baseline panel before that prescription is written, on our clinic page.
This article is for general education and is not medical advice. Any decision about starting or stopping testosterone therapy should be made with a urologist or endocrinologist who can review your full history and hormone results.
SwimScore uses CLIA-certified labs for all semen analysis and hormone testing, assessed against WHO 6th Edition clinical thresholds.
