Which testicular length measurement is likely correct for a male of reproductive age with oligospermia (sperm count of 56 million/ml) and a follicle-stimulating hormone (FSH) level of 9.9, after two ultrasounds 6 weeks apart showed different lengths of 4cm and 3.1cm?

Testicular Measurement Discrepancy: Which Ultrasound is Correct?

The 4cm measurement is almost certainly correct, and the 3.1cm measurement likely represents technical error in caliper placement during ultrasound. Your sperm count of 56 million/ml and FSH of 9.9 IU/L are entirely consistent with a 4cm testicular length, making severe testicular atrophy (which 3.1cm would suggest) extremely unlikely 1.

Why the 4cm Measurement is Reliable

A 4cm testicular length corresponds to a volume of approximately 15-18ml, which is considered normal and strongly correlates with your documented sperm production 1. The American College of Radiology notes that technical error in caliper placement during ultrasound is a common cause of incorrect testicular measurements, which can lead to falsely low volume calculations 1.

• Your sperm concentration of 56 million/ml exceeds the WHO reference limit of 16 million/ml by more than 3-fold, confirming adequate spermatogenesis 2, 1
• Testicular volume strongly correlates with total sperm count and sperm concentration 1
• A 3.1cm testis would calculate to approximately 8-10ml volume using the Lambert formula (Length × Width × Height × 0.71), which would be definitively atrophic and inconsistent with your sperm count 1

Your FSH Level Supports the 4cm Measurement

An FSH of 9.9 IU/L indicates borderline-elevated testicular reserve but is entirely compatible with normal sperm production 1, 3. This level does not suggest the severe testicular dysfunction that a 3.1cm testis would imply.

• FSH >7.6 IU/L is associated with non-obstructive azoospermia only when accompanied by testicular atrophy AND absent sperm production 3
• Your documented normal sperm count proves that despite borderline FSH, your testes are functioning adequately 1
• Men with true severe testicular atrophy (volumes <12ml) typically have FSH levels much higher than 9.9 IU/L and severely impaired sperm counts 1, 3

Common Ultrasound Measurement Pitfalls

Technical factors frequently cause measurement discrepancies between ultrasounds 1:

• Caliper placement error: Incorrect positioning of measurement calipers is the most common source of error, particularly for width measurements 1
• Inter-operator variability: Different sonographers using different techniques can produce measurements varying by 0.5-1.0cm 1
• Probe frequency differences: High-frequency probes (>10 MHz) provide more accurate measurements than lower frequency probes 1
• Measurement plane inconsistency: Measurements must be taken on true axial slices; oblique cuts systematically underestimate dimensions 1

What You Should Do Next

Request a repeat scrotal ultrasound with explicit attention to proper measurement technique to confirm testicular volume 1:

• Use high-frequency probes (>10 MHz) to maximize resolution 1
• Ensure measurements include three perpendicular dimensions (length, width, height) on axial slices 1
• Calculate volume using the Lambert formula (0.71 coefficient), not the traditional ellipsoid formula (0.52 coefficient) which systematically underestimates volume by 20-30% 1
• Compare measurements to the contralateral testis, as size discrepancy greater than 2ml or 20% warrants further evaluation 1

Clinical Context Matters

If you have normal fertility, no history of cryptorchidism, and normal secondary sexual characteristics, the likelihood of true severe testicular atrophy is extremely low 1. This further supports that the 3.1cm measurement represents technical error rather than biological reality.

• True biological change in testicular size over 6 weeks is extremely unlikely in adults unless there is acute pathology (trauma, torsion, infection) 1
• Your borderline FSH with normal sperm count represents mild testicular dysfunction, not the severe impairment that 3.1cm would suggest 1, 3

Important Monitoring Recommendation

Despite the measurement discrepancy being likely technical, your borderline FSH (9.9 IU/L) and oligospermia (56 million/ml is technically below the older 60 million/ml threshold) warrant monitoring 1, 4:

• Repeat semen analysis in 6 months to establish whether sperm parameters are stable or declining 4
• Obtain complete hormonal panel (LH, total testosterone, SHBG) to distinguish primary testicular dysfunction from secondary causes 1, 4
• Consider sperm cryopreservation if follow-up shows declining sperm concentration, especially if approaching 20 million/ml 4
• Avoid exogenous testosterone or anabolic steroids completely, as these suppress FSH and LH, causing azoospermia that can take months to years to recover 1, 4