Can small testicles (testicular hypoplasia) cause reduced semen production and impact fertility?

Small Testicles and Semen Production

Yes, small testicles (testicular hypoplasia) typically result in reduced semen production and impaired fertility, though the degree of impairment varies considerably—testicular volume strongly correlates with total sperm count and sperm concentration, with volumes below 12 mL considered atrophic and associated with significant spermatogenic dysfunction. 1, 2

Understanding the Relationship Between Testicular Size and Sperm Production

Normal vs. Atrophic Testicular Volume

• Testicular volumes less than 12 mL are definitively considered atrophic and associated with impaired spermatogenesis, reduced total sperm count, and decreased sperm concentration 1, 2
• Normal testicular volume ranges from 15-18 mL (corresponding to approximately 4 cm length), which is associated with normal spermatogenesis and adequate fertility potential 2
• Mean testicular size strongly correlates with total sperm count and sperm concentration—smaller testes produce fewer sperm 2

Clinical Patterns Based on Testicular Size

Men with testicular volumes of 10-12 mL typically have oligospermia (reduced sperm count) rather than complete azoospermia (no sperm), with FSH levels >7.6 IU/L indicating impaired but not absent spermatogenesis 2

• Testicular atrophy is a characteristic finding in non-obstructive azoospermia, where sperm production fails completely 1
• Even with small testes, up to 50% of men with non-obstructive azoospermia have retrievable sperm with microsurgical testicular sperm extraction (micro-TESE), despite elevated FSH levels 1

Hormonal Indicators of Testicular Dysfunction

FSH Elevation as a Marker

• Elevated FSH levels (>7.6 IU/L) strongly suggest testicular dysfunction and reduced sperm production, as FSH levels are negatively correlated with the number of spermatogonia 1
• Men with non-obstructive azoospermia typically present with low testicular volume, normal semen volume, and elevated FSH values 1
• FSH levels alone cannot definitively predict fertility status—hormonal levels have variable correlation with actual sperm retrieval outcomes 1

Diagnostic Evaluation

When small testicles are identified, the following evaluation is essential:

• Perform at least two semen analyses separated by 2-3 months to confirm the degree of oligospermia or azoospermia, as single analyses can be misleading due to natural variability 1, 2
• Measure serum FSH, LH, and testosterone to distinguish primary testicular failure from secondary hypogonadism 1, 2
• If sperm concentration is <5 million/mL, obtain karyotype analysis and Y-chromosome microdeletion testing (AZFa, AZFb, AZFc regions), as chromosomal abnormalities occur in 10% of these patients 1, 2

Causes of Testicular Hypoplasia

Genetic and Congenital Factors

• Karyotype abnormalities, including Klinefelter syndrome (47,XXY) and structural chromosomal anomalies, are established genetic causes of testicular hypoplasia and non-obstructive azoospermia 1
• Y-chromosome microdeletions, specifically in the AZFa, AZFb, and AZFc regions, are associated with impaired spermatogenesis—complete AZFa and AZFb deletions result in almost zero likelihood of sperm retrieval 1
• History of cryptorchidism (undescended testicles) is associated with smaller testicular volumes and impaired spermatogenesis 2

Acquired Factors

• Exogenous testosterone use completely suppresses spermatogenesis through negative feedback, potentially causing azoospermia that can take months to years to recover 1
• Exposure to certain toxins, such as lead and cadmium, and occupational exposures may contribute to testicular dysfunction 1

Fertility Implications and Management

Natural Conception Potential

• The combination of small testicular volume and elevated FSH indicates reduced testicular reserve, meaning decreased capacity to maintain sperm production if additional stressors occur 2
• Males are found to be solely responsible for 20-30% of infertility cases but contribute to 50% of cases overall 3
• Infertility is defined as failure to establish clinical pregnancy after 12 months of regular, unprotected sexual intercourse 3

Treatment Options

For men with small testes and confirmed oligospermia or azoospermia:

• Assisted reproductive technology (IVF/ICSI) offers superior pregnancy rates compared to empiric hormonal therapy and should be discussed early 1
• Microsurgical testicular sperm extraction (micro-TESE) is 1.5 times more successful than conventional TESE for sperm retrieval in non-obstructive azoospermia, with retrieval rates of 40-60% despite elevated FSH 4, 1
• Sperm cryopreservation should be considered if current sperm parameters are adequate, as men with reduced testicular reserve are at risk for progressive spermatogenic failure 2

Critical Pitfalls to Avoid

• Never prescribe exogenous testosterone to men desiring fertility—it provides negative feedback to the hypothalamus/pituitary, suppressing gonadotropin secretion and potentially causing complete azoospermia 1
• Avoid anabolic steroids completely, as these can suppress FSH and LH through negative feedback, causing azoospermia that can take months to years to recover 2
• Do not rely on a single semen analysis—repeat testing is essential to establish whether sperm parameters are stable or declining 1, 2

Additional Health Considerations

• Men with abnormal semen parameters have higher rates of testicular cancer and increased mortality rates compared to fertile men 2
• In men under 30 years with testicular volume <12 mL, there is a >34% risk of intratubular germ cell neoplasia (TIN) in the contralateral testis if testicular cancer is present 2
• Testicular self-examination should be taught given increased cancer risk with smaller testicular volumes 2