I've noticed my testicles have shrunk and my semen analysis shows a drop from about 56 million to 43 million sperm per ejaculate; should I expect a proportionally larger decline in sperm production?

Testicular Size Reduction and Sperm Count Decline: What to Expect

The decline in your sperm count from 56 million to 43 million per mL does NOT represent a proportionally larger decline than your testicular size reduction would predict—in fact, both values remain well within the normal fertile range, and testicular volume correlates with total sperm production but not in a simple linear fashion. 1, 2

Understanding Your Current Fertility Status

Your sperm concentration of 43 million/mL significantly exceeds the WHO lower reference limit of 16 million/mL (95% CI: 15-18 million/mL), placing you well within the normal fertile range 1, 3. However, research suggests that optimal fertility occurs with concentrations above 40 million/mL, and fecundity begins to decline progressively when sperm numbers drop below this threshold 1, 4, 5.

Key Points About Your Numbers:

• Sperm concentration of 43 million/mL is technically normal but represents the lower end of optimal fertility, as concentrations between 16-40 million/mL are associated with longer time to pregnancy compared to higher values 1
• The drop from 56 to 43 million/mL represents a 23% decline, which warrants investigation but does not indicate imminent progression to infertility 1
• Testicular volume strongly correlates with total sperm count and sperm concentration, but the relationship is not perfectly proportional—men with borderline-small testes (10-12 mL) typically have oligospermia rather than azoospermia 2, 6

Why Testicular Size and Sperm Count Don't Decline Proportionally

Testicular volumes less than 12 mL are generally considered small or atrophic and associated with impaired spermatogenesis, but even men with volumes of 10-12 mL typically maintain some sperm production rather than complete absence 2, 6. The seminiferous tubules (which produce sperm) occupy approximately 80% of testicular volume, but focal areas of preserved spermatogenesis can maintain sperm output even when overall testicular volume declines 2.

Critical Biological Variability:

• Semen parameters show significant intra-individual variability—the WHO strongly recommends obtaining at least two semen analyses separated by 2-3 months before drawing clinical conclusions, as single analyses can be misleading 7, 1
• Natural biological variation between samples is expected due to factors including abstinence duration (optimal 2-3 days), hydration status, recent illness, stress, and minor laboratory handling differences 1
• Multiple semen parameters must be evaluated together—concentration, motility, morphology, and volume—because combined assessment predicts fertility more accurately than concentration alone 1

What You Should Do Next

Immediate Actions:

• Obtain a repeat semen analysis in 2-3 months to establish whether your sperm parameters are stable or declining, as the WHO recommends at least two analyses separated by one month for accurate assessment 7, 1
• Ensure proper collection technique: 2-3 days abstinence before collection, transport sample at room or body temperature, and analyze within one hour of collection 1
• Measure hormonal panel: FSH, LH, total testosterone, and SHBG to calculate free testosterone, as this helps distinguish primary testicular dysfunction from secondary causes 2

If Follow-Up Shows Continued Decline:

• Consider sperm cryopreservation if concentration drops below 20 million/mL or approaches 15 million/mL, banking 2-3 separate ejaculates to provide backup samples and maximize future fertility options 2
• Genetic testing is indicated if sperm concentration falls below 5 million/mL with elevated FSH and testicular atrophy: karyotype analysis and Y-chromosome microdeletion screening (AZFa, AZFb, AZFc regions) 1, 2
• Scrotal ultrasound is recommended if there is a size discrepancy between testes greater than 2 mL or 20% to exclude pathology 2

Factors That Could Accelerate Decline

Avoid These Completely:

• Never use exogenous testosterone or anabolic steroids if fertility is desired—these completely suppress spermatogenesis through negative feedback on the hypothalamus and pituitary, causing azoospermia that can take months to years to recover 2, 6
• Chemotherapy or radiotherapy can cause additional impairment of semen quality for up to 2 years following treatment 2

Optimize These Modifiable Factors:

• Smoking cessation—cigarette smoking significantly reduces sperm volume and quality 8
• Maintain healthy body weight (BMI 18.5-25)—obesity (BMI >25) is associated with decreased sperm morphology, while underweight (BMI <18.5) reduces sperm concentration and total count 7, 8
• Limit alcohol consumption—drinking >10g per week decreases sperm volume and total numbers of morphologically normal and progressively motile sperm 8
• Minimize heat exposure to the testes—avoid hot tubs, saunas, and prolonged sitting 7
• Evaluate for varicocele on physical examination—correction of palpable varicoceles can improve both semen quality and fertility rates 2

Important Caveats

Even if testicular volume continues to decline, this does not guarantee proportional sperm count reduction or progression to azoospermia. Up to 50% of men with non-obstructive azoospermia and elevated FSH still have retrievable sperm via microsurgical testicular sperm extraction (micro-TESE), demonstrating that focal areas of spermatogenesis can persist despite overall testicular atrophy 2, 6.

Your current sperm count of 43 million/mL provides a total motile sperm count (TMSC) that likely exceeds 10 million per ejaculate (assuming normal motility), which is associated with good natural conception rates and indicates you should receive expectant management for 6-12 months if the female partner has good fertility prognosis 1.