Does Having One Testicle Affect Fertility?

Most men with one testicle can father children, but fertility is somewhat reduced compared to men with two. The degree of that reduction depends heavily on why the testicle was lost or is absent, whether to cancer, torsion, an undescended testicle, or trauma. The remaining testicle typically compensates by growing larger and ramping up sperm and hormone production, though this compensation has limits that show up clearly on semen analysis and hormone panels.

How the Remaining Testicle Compensates

When a boy is born with one testicle or loses one early in life, the remaining testicle usually undergoes what’s called compensatory hypertrophy: it physically enlarges and increases its output. Research on boys with congenital monorchism (born with one testicle) shows that markers of testicular function, particularly inhibin B, tend to normalize within the first two and a half years of life, reflecting this compensatory growth.¹ The process starts early and is driven by the brain’s hormonal feedback loop: with half the testicular tissue gone, the pituitary gland releases more follicle-stimulating hormone (FSH) to push the surviving testicle to work harder.

Studies of boys with compensatory testicular hypertrophy confirm that even before puberty, baseline FSH levels run higher than in boys with two testicles, and the FSH spike in response to hormonal stimulation is also larger.² This elevated FSH isn’t a sign of disease; it’s the body’s attempt to squeeze more function out of one testicle. In many cases it works well enough to keep sperm production and hormone levels in a functional range, though “functional” and “perfectly normal” aren’t the same thing.

What Semen Analysis Typically Shows

Even with compensatory growth, semen quality in men with one testicle tends to be lower than average. A study comparing men who had lost a testicle to surgical removal found that roughly half to just over half had sperm concentrations below 20 million per milliliter, regardless of whether the testicle was removed for cancer, torsion, or another reason.³ That 20-million threshold was the older World Health Organization cutoff for a “normal” count; the current lower reference limit is 16 million, but the point stands. A significant fraction of men with one testicle have sperm counts that sit below the range associated with easy conception.

Lower counts don’t automatically mean infertility. Plenty of men with below-average counts father children without any assistance. But when you combine a lower concentration with any additional hit to sperm motility or morphology, the odds of conceiving without help start to drop. Research on men who lost a testicle to germ cell tumors found that both seminoma and non-seminoma patients had lower sperm concentration and worse morphology compared to controls, even before any chemotherapy or radiation entered the picture.⁴ In other words, the underlying disease that led to the testicle’s removal may have already been damaging sperm quality before surgery.

When Cancer Is the Reason

Testicular cancer is one of the most common reasons a man ends up with a single testicle. The surgery itself, called radical orchiectomy, removes the affected testicle and typically leaves the remaining one intact. If treatment stops there, fertility prospects are reasonable: many men conceive naturally after orchiectomy alone. The trouble comes when additional treatment is needed.

Chemotherapy and radiation therapy can profoundly suppress sperm production in the remaining testicle. A study of 46 patients treated with post-operative radiation and/or chemotherapy for testicular cancer found that adjuvant treatment caused sterility in 17 patients who were previously known to be fertile. When the remaining testicle atrophied after treatment, the sterility was irreversible.⁵ Not every patient experienced permanent sterility; some recovered sperm production over the months and years following treatment. But the risk is real enough that sperm banking before starting chemotherapy or radiation is strongly recommended.

Among testicular cancer patients who had not conceived before treatment, about one in five banked their sperm, and roughly a quarter of those men later used the banked samples to conceive.⁶ That one-in-five banking rate is strikingly low given the stakes. If you’re facing orchiectomy for cancer and there’s any chance you’ll want biological children later, banking sperm before surgery or at least before any chemo or radiation is one of the most impactful decisions you can make. It’s fast, it’s widely available, and it preserves options that may otherwise disappear.

Undescended Testicle and Congenital Absence

Not all men with one functioning testicle lost it to surgery. Some were born with a testicle that never descended into the scrotum (cryptorchidism), and even after surgical correction in childhood, the undescended side may be nonfunctional or atrophied. Others are born with a genuinely absent testicle, a condition called congenital monorchism. The fertility picture for these men is different from post-surgical patients because the underlying cause often involves a developmental issue that can affect the remaining testicle too.

Reported paternity rates in men with a history of unilateral cryptorchidism land around two-thirds, compared to less than one-third for men who had bilateral undescended testes.⁷ A controlled study that compared men with a history of unilateral cryptorchidism to matched controls found that infertility was about twice as frequent in the cryptorchid group: roughly one in ten of the cryptorchid men who attempted paternity were unable to father children, versus about one in twenty of the controls.⁸ So the fertility hit is meaningful but not catastrophic for the unilateral cases. Most men with one undescended testicle do eventually become fathers, though they’re more likely than average to need help getting there.

Early surgical correction matters. The longer a testicle stays in the abnormal position, the more heat-related damage it sustains, and that damage can extend to the contralateral (opposite-side) testicle through mechanisms that researchers are still working out. Guidelines have shifted toward earlier orchiopexy (the surgery to bring the testicle down) in part because of fertility data showing better outcomes with earlier intervention.

After Testicular Torsion

Testicular torsion, where the spermatic cord twists and cuts off blood supply, is a urological emergency most common in adolescents. If the testicle can’t be saved, it’s removed. The reassuring news is that fertility outcomes after torsion-related orchiectomy are generally good. In a study tracking couples where the male partner had lost a testicle to torsion, about 84% achieved a successful first pregnancy resulting in a live birth. Among men whose torsed testicle was saved by surgical repositioning, the rate was slightly higher at about 91%, though the difference between groups wasn’t statistically significant.⁹

There’s an ongoing debate, however, about whether torsion damages the opposite testicle even when it’s left untouched. Animal research has demonstrated that unilateral torsion decreases blood flow and oxygen levels in the contralateral testicle, suggesting a mechanism for damage beyond the twisted side.¹⁰ Histological abnormalities in the opposite testicle have been reported in some human case series, but the evidence remains limited because most human studies are small.¹¹ In practice, the pregnancy data suggest that any contralateral damage, if it occurs, doesn’t prevent the majority of these men from fathering children.

The Antisperm Antibody Question

One mechanism that could theoretically harm fertility after losing a testicle is the formation of antisperm antibodies. Sperm cells are normally shielded from the immune system by a barrier within the testicle. When that barrier is disrupted through torsion, trauma, or surgery, the immune system encounters sperm proteins for the first time and may generate antibodies against them. Those antibodies can then attack sperm produced by the remaining testicle, impairing motility and the ability to fertilize an egg.

Animal models have clearly demonstrated this effect. Rats subjected to unilateral testicular torsion developed antibodies in the contralateral testicle, with immunoglobulin deposits identified on the basement membrane of the tubules where sperm are produced.¹² The antibodies appeared in animals that experienced torsion lasting 12 or 24 hours followed by detorsion, meaning even when the twisted testicle was untwisted rather than removed, the immune response was triggered.

Translating these animal findings to humans is tricky. The immune response varies widely between individuals, and antisperm antibodies are present in a subset of men with fertility problems regardless of whether they have one testicle or two. For men who’ve lost a testicle to torsion or trauma and are struggling to conceive, antisperm antibody testing is worth discussing with a reproductive specialist. When antibodies are a significant factor, treatments like intrauterine insemination or in vitro fertilization can bypass the problem.

Hormonal Shifts Worth Knowing About

Testosterone gets most of the public attention when men worry about losing a testicle, but the hormone story is more nuanced than just checking a testosterone level. A study comparing men with a solitary testicle to men with two found that median testosterone levels were essentially the same between the groups (around 381 versus 387 nanograms per deciliter). However, FSH was significantly higher in the solitary testicle group, and about 28% of men with one testicle had what’s called compensated hypogonadism, meaning their luteinizing hormone was elevated but their testosterone was still in the normal range, compared to only about 8% of men with two testes.¹³

Compensated hypogonadism is a kind of early warning state. The pituitary is working harder than usual to maintain normal testosterone output, and the remaining testicle is running at or near its ceiling. For many men this situation remains stable for years or decades, and they never notice symptoms. But it means the hormonal reserve is thinner. If the remaining testicle suffers any additional insult, whether from illness, medication, weight gain, or aging, testosterone levels could drop below the normal range faster than they would in a man with two testes. Periodic hormone checks are a reasonable precaution, especially as men with a solitary testicle move into their forties and fifties.

One critical practical point: if you have one testicle and your testosterone is on the low side, be cautious about testosterone replacement therapy. Exogenous testosterone signals the brain to shut down its own hormonal signals to the testicle, which suppresses sperm production. In a man with two testes, this suppression is usually reversible when the testosterone is stopped. In a man with one testicle already running near capacity, the recovery may be slower or incomplete. If fertility is a priority, a reproductive endocrinologist can explore alternatives that support testosterone without shutting down sperm production.

How Age at Loss Affects the Outlook

Whether the testicle was lost in infancy, during adolescence, or in adulthood matters more than people realize. Boys who are born with one testicle or lose one very early in life have the advantage of going through puberty with an already-compensated single testicle. The remaining testicle has had years to grow and ramp up production before fertility ever becomes relevant. For these men, semen parameters may be lower than average but are often adequate for natural conception.

Adolescents who lose a testicle to torsion during the critical window of puberty face a somewhat more complex recovery, because the remaining testicle has to compensate while simultaneously maturing. Still, the pregnancy data from torsion studies are encouraging: age at torsion did not produce statistically significant differences in pregnancy rates, and the vast majority of men achieved conception regardless of whether the event happened during or after puberty.⁹

Adults who lose a testicle to cancer or trauma face the most abrupt adjustment. There’s no years-long compensatory growth period; the remaining testicle must ramp up quickly, and any additional treatment like chemotherapy can hit before the body has fully adapted. This is one more reason early sperm banking is so valuable in adults facing orchiectomy.

When to See a Specialist

Having one testicle doesn’t automatically mean you need a fertility workup. If you’re not trying to conceive, and your energy levels, libido, and general health feel normal, you can simply keep up with regular checkups and mention your single-testicle status so your doctor can monitor hormone levels periodically. But if you’ve been actively trying to conceive for six months to a year without success, a semen analysis is a logical first step. It’s inexpensive, noninvasive, and gives a clear snapshot of sperm count, motility, and morphology.

Beyond semen analysis, a hormone panel checking FSH, LH, and testosterone can reveal whether you’re in that compensated hypogonadism zone. If sperm counts are very low or hormones are significantly off, a reproductive urologist can discuss options ranging from lifestyle modifications and hormonal treatments to assisted reproductive technologies like intrauterine insemination or in vitro fertilization with intracytoplasmic sperm injection. The odds of eventually having biological children remain high for most men with one testicle, especially when they’re proactive about understanding their baseline numbers and seeking help early rather than waiting years before getting evaluated.

Protecting the Remaining Testicle

Men with a solitary testicle carry a practical concern that men with two don’t have to think about: there’s no backup. An injury, infection, or torsion event affecting the remaining testicle could end both hormone production and fertility at once. Athletic cups during contact sports aren’t just sensible advice for these men; they’re genuinely important protection. Torsion in the remaining testicle is a true emergency with higher stakes than normal, and anyone experiencing sudden, severe testicular pain should get to an emergency room immediately rather than waiting to see if it resolves.

Infections like epididymitis or orchitis can also damage testicular tissue. Mumps orchitis, though less common in the vaccination era, is one of the classic threats. Staying current on vaccinations and treating urinary tract or sexually transmitted infections promptly reduces the risk of infectious damage to the remaining testicle. These aren’t exotic precautions; they’re the kind of basic health maintenance that takes on extra significance when you’re relying on a single organ to do the work of two.