A man can generally reproduce with only one testicle. This condition, known as monorchism, does not automatically equate to infertility. The vast majority of men with a single testis maintain the ability to father children because the remaining gland is capable of compensating for the loss. The single gonad often maintains the reproductive process, including both hormone production and sperm generation, at a functional level.
The Biological Mechanism of Compensation
The human reproductive system exhibits a capacity for compensation after the loss of one testicle. The remaining testicle often undergoes compensatory hypertrophy, where it enlarges to meet the body’s physiological demands. This increase in size is a physical manifestation of its heightened functional activity.
The single testicle must fulfill the dual roles normally performed by two: producing testosterone and generating sperm. Testosterone production, responsible for male characteristics and sexual function, is usually maintained at normal levels by the remaining Leydig cells. This sustained hormone output is crucial for overall health and the final stages of sperm maturation.
Spermatogenesis, the process of sperm production, is driven by hormonal signals from the pituitary gland. The body responds to the absence of one testicle by increasing the output of Follicle-Stimulating Hormone (FSH), which acts directly on the remaining Sertoli cells. This elevated stimulation enhances the efficiency and capacity of the single testicle to produce adequate sperm.
While hormonal balance is often maintained, this compensation requires the remaining testicle to work harder, sometimes referred to as compensated pituitary strain. Studies show that even with elevated FSH levels, which indicate this increased strain, the remaining testicle can still produce sperm. This physiological adaptation allows many men with monorchism to achieve fertility rates similar to the general population.
Causes of Having Only One Testicle
A male may have only one testicle due to conditions present from birth (congenital) or acquired circumstances later in life. Congenital monorchism means the absence of one testicle was present at birth. This can be caused by the failure of the testicle to form (gonadal agenesis) or, more commonly, by vanishing testis syndrome, where the testicle regresses in utero, often due to a vascular event.
Another congenital factor is cryptorchidism, or an undescended testicle, which may require surgical removal (orchiectomy) if it is damaged. Acquired causes result from events after birth. These include surgical removal due to testicular cancer, severe trauma, or loss following severe infection or testicular torsion, where the spermatic cord twists and cuts off blood supply.
Regardless of the cause, the remaining testicle’s ability to function independently is the main factor determining reproductive potential. The prognosis for fertility is more dependent on the health and compensatory capacity of the single remaining gland than on the original cause of the loss.
Evaluating Fertility and Success Rates
Evaluating fertility for men with a single testicle begins with a comprehensive semen analysis, which assesses the quality and quantity of sperm produced. This test measures key parameters such as sperm concentration, motility (movement), and morphology (shape). While the remaining testicle is often highly functional, some men may exhibit sub-optimal sperm concentrations.
The success rate of reproduction can be influenced by the health of the remaining testicle and previous medical treatments. For example, men who lost a testicle due to cancer may have had chemotherapy or radiation, which can impair the function of the remaining sperm-producing cells. If the cause was uncorrected cryptorchidism, the remaining testicle may have been affected by the same underlying developmental issues.
If a couple has been trying to conceive without success, the standard recommendation is to seek a fertility evaluation after 12 months of regular, unprotected intercourse. A fertility specialist can review the semen analysis, assess hormonal status, and determine if assisted reproductive techniques, such as intrauterine insemination (IUI) or in-vitro fertilization (IVF), are needed. Most men with a single testicle will not require intervention to achieve a pregnancy.
Long-Term Health and Monitoring
Long-term health management for men with a single testicle focuses on endocrine function and cancer screening. Although the remaining testicle usually produces sufficient testosterone, regular blood tests are prudent to monitor hormone levels. A decline in testosterone, though uncommon when the remaining testicle is healthy, can lead to symptoms like fatigue and decreased sexual desire.
If testosterone levels fall below the normal range (hypogonadism), replacement therapy may be recommended to prevent long-term health issues. Men with a history of testicular cancer or cryptorchidism face a higher risk of developing cancer in the remaining testicle. Monthly testicular self-examinations are advised to detect any changes early. Regular urological monitoring ensures that any potential issues with the remaining testicle are identified and treated promptly.