Do smaller testicles in a male of reproductive age indicate infertility?

Testicular Size and Male Fertility

Smaller testicles do not automatically mean infertility, but testicular volumes below 12 mL are strongly associated with impaired sperm production and warrant immediate evaluation. 1

Understanding the Relationship Between Testicular Size and Fertility

Normal adult testicular volume ranges from 15-25 mL, with volumes below 12 mL considered pathologically small (testicular atrophy). 1, 2 The relationship between testicular size and fertility is not absolute—many men with smaller testicles maintain adequate sperm production, while testicular atrophy combined with elevated FSH levels (>7.6 IU/L) strongly suggests spermatogenic failure. 1, 3

Key Clinical Patterns

• Testicular atrophy with elevated FSH (>7.6 IU/L) indicates primary testicular dysfunction and significantly reduced sperm production, though not necessarily complete absence of sperm. 1, 3

• Even with non-obstructive azoospermia and testicular atrophy, up to 50% of men still have retrievable sperm via microsurgical testicular sperm extraction (micro-TESE). 1

• Infertile men with varicoceles demonstrate smaller bilateral testicular volumes (right: 18.7 cm³, left: 17.6 cm³) compared to fertile men with varicoceles (right: 25.2 cm³, left: 21.6 cm³) or fertile controls (right: 24.9 cm³, left: 23.4 cm³). 4

Essential Diagnostic Evaluation

When testicular volumes are below 12 mL, the following workup is mandatory:

• Obtain at least two semen analyses separated by 2-3 months, as single analyses are misleading due to natural variability. 1

• Measure morning FSH, LH, and total testosterone on two separate occasions to distinguish primary testicular failure (elevated FSH/LH with low testosterone) from secondary hypogonadism (low FSH/LH with low testosterone). 1

• Perform karyotype analysis and Y-chromosome microdeletion testing (AZFa, AZFb, AZFc regions) if sperm concentration is below 5 million/mL or azoospermia is confirmed. 1, 3

• Physical examination must assess for varicoceles, as testicular size discrepancy is twice as common in infertile men with varicoceles (32%) versus those without (17%). 5

Critical Hormonal Thresholds

• FSH >7.6 IU/L with testicular atrophy strongly suggests non-obstructive azoospermia or severe oligospermia, though this does not preclude all sperm production. 1

• Infertile men with varicoceles have significantly higher FSH levels (7.8 ± 7.6 IU/L) compared to fertile men with varicoceles (3.5 ± 2.1 IU/L) or fertile controls (3.5 ± 1.9 IU/L). 4

• Normal LH and testosterone levels with mildly elevated FSH suggest oligospermia rather than complete testicular failure. 1

Common Causes of Testicular Atrophy

Reversible causes must be identified and corrected before concluding permanent infertility:

• Exogenous testosterone or anabolic steroid use causes reversible testicular atrophy and azoospermia through negative feedback suppression—immediate discontinuation is essential if fertility is desired. 1, 3

• Varicoceles are the most common reversible cause, with repair potentially improving testicular volume, reducing FSH, and improving sperm parameters. 1, 4

• History of cryptorchidism (undescended testicles) results in permanently smaller, "incompetent" testes even after surgical correction, with markedly elevated sterility rates. 6

• Klinefelter syndrome (47,XXY) is the most frequent genetic cause, presenting with small firm testes, elevated FSH, and azoospermia or severe oligospermia. 1, 6

• Prior mumps orchitis, testicular torsion, chemotherapy, or radiation causes irreversible testicular damage and atrophy. 6

Fertility Preservation Strategies

For men with testicular volumes below 12 mL and documented sperm production:

• Bank sperm immediately—collect 2-3 separate ejaculates with 2-3 days abstinence between collections—before any intervention or while parameters remain stable. 1

• Once azoospermia develops, even micro-TESE only achieves 40-50% sperm retrieval rates, making preemptive cryopreservation critical. 1, 3

• Avoid all exogenous testosterone, anabolic steroids, and gonadotoxic medications, as these can cause complete azoospermia requiring months to years for recovery. 1

Varicocele Management

For palpable varicoceles with testicular atrophy and abnormal semen parameters:

• Varicocele repair can halt progression of testicular atrophy, potentially reverse some damage, improve testosterone levels, reduce FSH, and stabilize testicular volume. 1

• Repair is most effective when performed before irreversible testicular injury occurs, with 69% of men with zero motile sperm before surgery achieving motile sperm post-operatively. 1

• Do not treat subclinical varicoceles found only on ultrasound—only palpable varicoceles improve fertility outcomes after repair. 3

Cancer Surveillance Considerations

Testicular atrophy increases cancer risk and requires monitoring:

• Men with testicular volumes below 12 mL, particularly those under age 30-40 with history of cryptorchidism, have significantly increased risk of intratubular germ cell neoplasia (>34% if testicular cancer develops). 3, 2

• Perform monthly testicular self-examination to detect hard lumps, masses, or sudden size changes requiring immediate evaluation. 2

• Testicular microcalcifications on ultrasound increase cancer risk 18-fold in men with testicular atrophy and warrant consideration of testicular biopsy. 3

Critical Pitfalls to Avoid

• Never prescribe testosterone replacement therapy if current or future fertility is desired—it will completely suppress spermatogenesis through negative feedback, causing azoospermia. 1, 3

• Do not rely on a single semen analysis—natural variability requires at least two analyses separated by 2-3 months for accurate diagnosis. 1, 3

• Testicular size discrepancy alone does not predict infertility—82% of men with left varicoceles and testicular atrophy remain fertile, so size difference without hormonal abnormalities or abnormal semen analysis does not mandate intervention. 7

• FSH levels alone cannot definitively predict fertility status—men with maturation arrest can have normal FSH despite severe spermatogenic dysfunction, while others with elevated FSH maintain adequate sperm production. 1