Study analysis · Andrologia · 2018
Your right testicle might be the key to your fertility — and it's not what you think.
If your right testicle is smaller than a golf ball, you're nearly three times more likely to have low sperm count or low testosterone.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study looked at guys who went to the doctor because they were having trouble having babies, and found that guys with bigger right testicles tended to have better sperm and more hormones. But it doesn't prove that a bigger testicle makes those things better — it just shows they often go together.
What’s the bottom line?
Doctors measured both testicles in men trying to have babies and found that the right one’s size was a better clue about sperm and hormone levels, even though both testicles were usually the same size.
How strong is this study?
The study measured things carefully with ultrasounds and blood tests, which is good. But since they only looked at people who already went to the clinic, and didn't randomly assign anyone to have bigger or smaller testicles, we can't be sure the results apply to everyone — it's like guessing what all kids like to eat by only asking kids who already like broccoli.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
38 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=301)+15.6/20
- Follow-upno follow-up reported
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervals+15/15
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 544 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
This design cannot establish causation — the findings describe an association, not a cause. This is an observational cross-sectional study with no randomization or intervention; it measures associations at a single point in time and cannot determine whether testicular volume causes changes in sperm or testosterone levels, or vice versa.
No Conflicts
No conflicts of interest identified
No conflicts of interest identified; funding came from public research foundations with no indication of industry influence or author ties to commercial entities.
Funders
Conflict Details
National Natural Science Foundation of China: Received grant funding for the study
Incubating Program for Clinical Research and Innovation of Ren Ji Hospital: Received grant funding for the study
National Natural Science Foundation of China: Received grant funding for the study
Incubating Program for Clinical Research and Innovation of Ren Ji Hospital: Received grant funding for the study
National Natural Science Foundation of China: Received grant funding for the study
+9 more conflicts
All authors are affiliated with academic institutions; no industry ties, employment, or financial interests in commercial entities were disclosed. The study appears to be independently conducted with public funding.
Key takeaways
- 01
If the right testicle is smaller than 15 mL, there’s a 2.79x higher chance of low sperm count or low testosterone.
- 02
It correctly flagged poor function in 67% of cases.
- 03
Yes — a small right testicle could help doctors spot fertility problems without invasive tests, though it’s not perfect.
Surprising findings
- Right testicular volume was the only independent predictor of low testicular function, despite no overall size difference between testes.Doctors and patients assume both testicles are interchangeable — but this study shows the right one has unique predictive power, which contradicts the assumption of bilateral symmetry in reproductive function.
- RTV <15 mL had a 2.79x higher odds of impaired function — stronger than expected for a single non-invasive metric.Most clinical indicators require bloodwork or semen analysis; this single ultrasound measurement outperformed many in predictive power despite being simple and cheap.
Practical takeaways
If you're trying to conceive and have concerns, ask your urologist to measure your right testicular volume via ultrasound — a value under 15 mL may signal the need for further testing.
This only applies to men already seeking fertility evaluation; it's not a diagnostic tool for the general population and doesn't prove causation.
medium confidenceWhy this study matters
Right Testicle Rules
Despite both testicles being the same average size, the right testicular volume (RTV) showed stronger correlations with sperm concentration (β=0.292, p<0.001), motility (β=0.227, p<0.001), and testosterone (β=0.245, p<0.001) than the left. RTV under 15 mL was the only independent predictor of impaired testicular function (OR=2.79).
Most people assume both testicles are equally important — but this study suggests your right one might be the real indicator of fertility health, even when they look identical.
The 15 mL Threshold
A right testicular volume below 15 mL predicted low testicular function with 66.7% sensitivity and 62.4% specificity — meaning it correctly flagged problems in nearly 2 out of 3 cases without blood tests or biopsies.
This could mean a simple ultrasound scan — not expensive hormone panels — might help men quickly identify potential fertility issues.
No Size Difference, But Big Difference in Meaning
The study found no average size difference between left and right testicles — yet only RTV was statistically significant in predicting sperm and hormone levels. This suggests function isn't just about size, but which side's size matters more.
It challenges the assumption that symmetry equals equality — biology might favor one side for diagnostic value, even if they look the same.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Doctors measured both testicles in men trying to have babies and found that the right one’s size was a better clue about sperm and hormone levels, even though both testicles were usually the same size.
Research results
If the right testicle is smaller than 15 mL, there’s a 2.79x higher chance of low sperm count or low testosterone. It correctly flagged poor function in 67% of cases.
What this means - more context
Yes — a small right testicle could help doctors spot fertility problems without invasive tests, though it’s not perfect.
This study evaluates whether left or right testicular volume better predicts testicular function in men undergoing fertility evaluation.
Right testicular volume (RTV) showed stronger independent associations with sperm concentration, motility, and total testosterone than left testicular volume, despite no average size difference between testes. RTV <15 mL predicted low testicular function with 66.7% sensitivity and 62.4% specificity, and was the only significant predictor of impaired function (OR=2.79).
Methods Used
Cross-sectional study of 301 men (274 with oligoasthenozoospermia/low testosterone, 27 controls); testicular volume measured via scrotal ultrasound; semen analysis and hormone levels assessed; stepwise linear and logistic regression used to determine predictive value.
Main Finding
Right testicular volume <15 mL was the only independent predictor of low testicular function (OR=2.79, 95% CI: 1.18–6.66, p=0.020), with RTV showing stronger correlations than left volume with sperm concentration (β=0.292, p<0.001), motility (β=0.227, p<0.001), and total testosterone (β=0.245, p<0.001).
Confidence Level
Moderate; findings are statistically robust with reported effect sizes and confidence intervals, but limited by cross-sectional design and lack of causal inference.
Study Flags
Red Flags
- •Cross-sectional design cannot prove causation
- •No adjustment for potential confounders like varicocele or lifestyle factors
- •Sample limited to men seeking fertility care, limiting generalizability
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Surprising Findings
Right testicular volume was the only independent predictor of low testicular function, despite no overall size difference between testes.
Doctors and patients assume both testicles are interchangeable — but this study shows the right one has unique predictive power, which contradicts the assumption of bilateral symmetry in reproductive function.
Practical Takeaways
If you're trying to conceive and have concerns, ask your urologist to measure your right testicular volume via ultrasound — a value under 15 mL may signal the need for further testing.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 544 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Human Cross-Sectional
Subject
Moderate probability
on the GRADE evidence scale
This study looked at guys who went to the doctor because they were having trouble having babies, and found that guys with bigger right testicles tended to have better sperm and more hormones. But it doesn't prove that a bigger testicle makes those things better — it just shows they often go together.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Clear inclusion/exclusion criteria
- Use of standardized ultrasound for testicular volume measurement
- Objective laboratory measures (semen analysis, hormone levels)
Weaknesses
- Cross-sectional design prevents determination of temporal sequence
- No randomization or control of confounding variables beyond statistical adjustment
- Blinding status unknown, risking measurement or reporting bias
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Doctors measured both testicles in men trying to have babies and found that the right one’s size was a better clue about sperm and hormone levels, even though both testicles were usually the same size.
Research results
If the right testicle is smaller than 15 mL, there’s a 2.79x higher chance of low sperm count or low testosterone. It correctly flagged poor function in 67% of cases.
What this means - more context
Yes — a small right testicle could help doctors spot fertility problems without invasive tests, though it’s not perfect.
This study evaluates whether left or right testicular volume better predicts testicular function in men undergoing fertility evaluation.
Right testicular volume (RTV) showed stronger independent associations with sperm concentration, motility, and total testosterone than left testicular volume, despite no average size difference between testes. RTV <15 mL predicted low testicular function with 66.7% sensitivity and 62.4% specificity, and was the only significant predictor of impaired function (OR=2.79).
Methods Used
Cross-sectional study of 301 men (274 with oligoasthenozoospermia/low testosterone, 27 controls); testicular volume measured via scrotal ultrasound; semen analysis and hormone levels assessed; stepwise linear and logistic regression used to determine predictive value.
Main Finding
Right testicular volume <15 mL was the only independent predictor of low testicular function (OR=2.79, 95% CI: 1.18–6.66, p=0.020), with RTV showing stronger correlations than left volume with sperm concentration (β=0.292, p<0.001), motility (β=0.227, p<0.001), and total testosterone (β=0.245, p<0.001).
Confidence Level
Moderate; findings are statistically robust with reported effect sizes and confidence intervals, but limited by cross-sectional design and lack of causal inference.
Study Flags
Red Flags
- •Cross-sectional design cannot prove causation
- •No adjustment for potential confounders like varicocele or lifestyle factors
- •Sample limited to men seeking fertility care, limiting generalizability
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Surprising Findings
Right testicular volume was the only independent predictor of low testicular function, despite no overall size difference between testes.
Doctors and patients assume both testicles are interchangeable — but this study shows the right one has unique predictive power, which contradicts the assumption of bilateral symmetry in reproductive function.
Practical Takeaways
If you're trying to conceive and have concerns, ask your urologist to measure your right testicular volume via ultrasound — a value under 15 mL may signal the need for further testing.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 544 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Human Cross-Sectional
Subject
Moderate probability
on the GRADE evidence scale
This study looked at guys who went to the doctor because they were having trouble having babies, and found that guys with bigger right testicles tended to have better sperm and more hormones. But it doesn't prove that a bigger testicle makes those things better — it just shows they often go together.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Clear inclusion/exclusion criteria
- Use of standardized ultrasound for testicular volume measurement
- Objective laboratory measures (semen analysis, hormone levels)
Weaknesses
- Cross-sectional design prevents determination of temporal sequence
- No randomization or control of confounding variables beyond statistical adjustment
- Blinding status unknown, risking measurement or reporting bias
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study measured things carefully with ultrasounds and blood tests, which is good. But since they only looked at people who already went to the clinic, and didn't randomly assign anyone to have bigger or smaller testicles, we can't be sure the results apply to everyone — it's like guessing what all kids like to eat by only asking kids who already like broccoli.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
38 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=301)+15.6/20
- Follow-upno follow-up reported
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervals+15/15
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 544 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
This design cannot establish causation — the findings describe an association, not a cause. This is an observational cross-sectional study with no randomization or intervention; it measures associations at a single point in time and cannot determine whether testicular volume causes changes in sperm or testosterone levels, or vice versa.
No Conflicts
No conflicts of interest identified
No conflicts of interest identified; funding came from public research foundations with no indication of industry influence or author ties to commercial entities.
Funders
Conflict Details
National Natural Science Foundation of China: Received grant funding for the study
Incubating Program for Clinical Research and Innovation of Ren Ji Hospital: Received grant funding for the study
National Natural Science Foundation of China: Received grant funding for the study
Incubating Program for Clinical Research and Innovation of Ren Ji Hospital: Received grant funding for the study
National Natural Science Foundation of China: Received grant funding for the study
+9 more conflicts
All authors are affiliated with academic institutions; no industry ties, employment, or financial interests in commercial entities were disclosed. The study appears to be independently conducted with public funding.