The question of whether having only one testicle, a condition known as monorchidism, impacts a man’s ability to conceive is a common concern. This condition can be present from birth (congenital) or acquired later in life due to injury, torsion, or the surgical removal of one testicle (orchiectomy). The primary worry centers on whether the remaining organ can adequately perform the dual functions of the testes: producing sperm for fertility and testosterone for overall health. The biological reality is complex and depends entirely on the health and compensatory capacity of the single remaining testicle.
The Role of the Remaining Testicle in Fertility
A healthy testicle is designed with a significant reserve capacity for both spermatogenesis (sperm creation) and steroidogenesis (testosterone production). When one testicle is removed or non-functional, the body’s hormonal feedback system signals the remaining testicle to increase its output, a mechanism known as compensation. This compensatory effort typically allows the single testicle to maintain sperm counts and hormone levels within the normal range required for conception and general well-being.
The pituitary gland in the brain releases higher amounts of Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH), which stimulate the testicle. In many cases, the single testicle will undergo a slight, measurable enlargement, termed compensatory hypertrophy, as it adjusts to its increased workload.
For the majority of men with a healthy, solitary testicle, fertility rates are similar to those of men with two testicles. Studies show that a single healthy testicle is generally capable of producing sufficient sperm concentration, motility, and morphology to achieve natural pregnancy.
Specific Conditions That Reduce Function
While a single testicle often compensates successfully, the reasons for having only one, or the underlying health of the remaining one, can introduce specific risks to fertility. If the remaining testicle was previously undescended, a condition called cryptorchidism, its long-term sperm-producing function may be inherently lower.
Even after surgical correction, a previously maldescended testicle may have residual damage to the germ cells, the precursors to sperm, leading to a reduced capacity for spermatogenesis. This internal damage means the remaining testicle is starting from a lower functional baseline. Similarly, men who lost a testicle due to testicular torsion may have reduced fertility even in the remaining testicle, potentially due to a pre-existing abnormality or an immunological reaction that affects both organs.
The most significant factors affecting the remaining testicle are often related to the treatment for the condition that necessitated the removal of the first. For example, chemotherapy or radiation used to treat testicular cancer can severely and sometimes permanently impair the sperm-producing cells in the remaining testicle. Men with a history of testicular cancer have a higher risk of abnormal semen parameters compared to the general population, suggesting that the underlying disease or associated factors can affect the health of both testes.
Evaluating Fertility and Hormone Levels
For men with a solitary testicle who are concerned about their reproductive capacity, a comprehensive medical evaluation is the necessary next step. The cornerstone of fertility assessment is a semen analysis, which measures several key factors of the ejaculate. This test quantifies the sperm concentration (count), the percentage of sperm showing progressive forward movement (motility), and the proportion of sperm with a normal shape (morphology).
The World Health Organization (WHO) provides reference ranges, and a count above 15 million sperm per milliliter is generally considered normal. When abnormalities are found, a specialist, typically a urologist or reproductive endocrinologist, can interpret these findings in the context of monorchidism.
Hormone testing is also performed to assess the function of the pituitary-testicular axis. Blood tests measure Follicle-Stimulating Hormone (FSH), Luteinizing Hormone (LH), and Testosterone (T) levels. A common pattern in men with a solitary testicle is compensated pituitary strain, characterized by elevated FSH and LH levels despite having normal or near-normal testosterone and semen parameters. If testosterone levels are low alongside high FSH and LH, it suggests primary testicular failure, indicating the remaining testicle cannot compensate adequately and may require further intervention.