Semen Analysis, Explained

Parameter explainer · Count

Concentration and total count: the floor, the plateau, and the thresholds that matter

Concentration is the number most people fixate on. It is also the one that swings most between tests, and the one where the WHO reference limit is most often mistaken for a target.

Two numbers, not one

Concentration is how many sperm are in each millilitre of semen. Total sperm number is concentration multiplied by volume: how many sperm were in the whole sample. Two men with the same concentration can have very different totals, which is why the WHO manual asks labs to report both.[2] "Oligozoospermia" means a concentration below the reference limit; "azoospermia" means no sperm were found.

Where your value sits

WHO 2021 distribution for concentration (million/mL). Example marker at 20 million/mL. Place your own value in the numbers box.
Measure5th25th50th75th95th
Concentration (million/mL)163066110208
Total sperm number (million)3996210363802
Semen volume (mL)1.42.13.04.26.2

The reference population is about 3,500 men whose partners conceived within 12 months.[1] The concentration limit moved from 15 to 16 million/mL in 2021, which is why older reports and many websites still print 15.[2]

Clinical sub-bands used by guidelines, which are not WHO centiles: below 16 million/mL is oligozoospermia; below 5 million/mL is severe, and the point where genetic testing enters; at or below 1 million/mL is where Y-chromosome microdeletion testing is strongest.

What it predicts, and what it does not

The chance of conception rises with concentration, then flattens. In 430 Danish couples trying for a first pregnancy, the probability of conceiving per cycle increased with concentration up to about 40 million/mL and did not rise further above that.[3] In a modern cohort of 6,061 men, concentration of 35 million/mL or more and total count of 95 million or more were associated with faster conception (hazard ratios about 1.5), and the authors noted these "optimal" values sit well above the WHO 5th centile, which is a lower bound rather than a target.[5]

Fertile and infertile ranges overlap. In 696 fertile and 765 infertile couples, concentration above 48 million/mL was "fertile range" and below 13.5 "subfertile range"; the odds of being in the infertile group were 5.3 times higher in the subfertile band, yet none of the measures was diagnostic on its own.[4]

Total motile sperm count predicts better than concentration alone. In 1,177 couples followed for three years, TMSC bands of under 5, 5–20 and over 20 million separated spontaneous pregnancy chances more cleanly than any single WHO parameter.[6] The motility explainer shows the arithmetic.

Total sperm number (million per ejaculate). Example marker at 60 million (3 mL × 20 million/mL).

Why one test is a snapshot

Concentration is the most variable number on the report within the same man: in 74 infertile men giving 479 samples, the within-subject coefficient of variation was 54%; in 65 donors it was 46%. At least three samples were needed to characterize a man reliably.[7] A swing from 8 to 16 million/mL between two tests is ordinary biology, not necessarily a change in health.

Collection conditions move the number too. Across 13 randomized trials, samples after 3 or more days of abstinence had about 9 million/mL higher concentration and 1 mL more volume than samples after under 2 days.[9] Sperm production itself takes an average 64 days, so a fever or heat exposure two to three months ago can show up today.[8]

What can lower it

FactorWhat the evidence showsStrength
Short abstinence or incomplete sample+9 million/mL with 3 or more days of abstinence versus under 2.[9]Moderate (RCTs)
Clinical varicoceleRepair associated with +10 to +12 million/mL in pooled studies; pregnancy effect RR 1.55, low certainty; live birth uncertain.[15][16]Low to moderate
Testosterone, anabolic steroids, SARMsSuppress sperm production; guidelines advise against testosterone while trying to conceive.[10]Guideline
Genetic (Klinefelter, Y-microdeletions)Chromosomal abnormalities about ten times more common below 5 million/mL.[11]Guideline
Smoking−9.7 million/mL in smokers across 20 studies, 5,865 men.[12]Moderate (observational)
Excess weightOligozoospermia odds 1.4× in obese men; azoospermia 1.8×, across 14 studies.[13]Moderate (observational)
Scrotal heatTwice-weekly sauna for 3 months impaired count; fully reversed by 6 months after stopping.[14]Low (n=10)
Obstruction, prior vasectomy, absent vasLow volume plus very low count or azoospermia; sorted out by volume, pH, exam and FSH.[10]Guideline

What guidelines say to do next

  1. Repeat. Two analyses, about a month apart, same abstinence length. Azoospermia must be confirmed on two samples with centrifugation.[10][11]
  2. Hormones. FSH and testosterone when concentration is low or zero (AUA/ASRM Statement 10; EAU Strong).[10][11]
  3. Genetics. Karyotype with azoospermia or concentration below 5 million/mL when FSH is raised, testes are small, or impaired production is suspected; Y-chromosome microdeletion testing at or below 1 million/mL, considered below 5.[10][11]
  4. Azoospermia is a separate pathway: first separate obstruction from impaired production using volume, pH, exam and FSH.[10]
  5. Varicocele. Consider repair when palpable, with infertility and abnormal semen parameters; not for subclinical varicocele.[10][11]
  6. Treatment route. With a low total motile sperm count on repeated analyses, IUI success may be reduced and IVF/ICSI may be considered (Statement 39, Expert Opinion).[10]
  7. Not recommended: testosterone while trying; routine DNA fragmentation testing at the first visit; supplements as a treatment plan. Cochrane 2022: a very-low-certainty live-birth signal that disappears once biased trials are removed.[10][17]

Ask for a prompt specialist review if: any report shows zero sperm; concentration is below 5 million/mL; volume is low (under 1.4 mL) together with a low count; you have used testosterone, anabolic steroids or SARMs; or there is a history of undescended testis, chemotherapy, or a scrotal mass.

Questions to bring to your doctor

  • What was my total sperm number (concentration × volume), not just the concentration?
  • How many days of abstinence did I have, and was the sample complete? Should the repeat match that?
  • Is my concentration below 16, below 5, or at or below 1 million/mL? Which tests does each level trigger?
  • Have FSH, LH and testosterone been checked? What were the values?
  • Do I need karyotype or Y-microdeletion testing based on my count?
  • Did the physical exam find a varicocele, and is it palpable?
  • What is my total motile sperm count, and where does it sit against the 5 and 20 million bands?
  • Am I taking anything (testosterone, finasteride, opioids, supplements) that could suppress production?

Things people hear, and what the evidence says

"My count doubled in two months on supplements."
Within-man variation for count is about 50%, and abstinence differences alone can add 9 million/mL. A doubling between two tests is within normal fluctuation.
"15 million is the cut-off."
The WHO 2021 lower reference limit is 16 million/mL. Some labs still print 15 or older ranges; that is a reporting lag, not a different biology.
"A low count means I need IVF."
Guidelines route by total motile count on repeated tests, hormones and examination. TMSC over 20 million behaved like normal in outcome data.
"I'll take testosterone to boost my sperm."
Testosterone shuts down sperm production. Guidelines advise against it for men trying to conceive.

Sources

Each claim above carries a bracketed number pointing here. "Primary" means the full paper or guideline text was read; "abstract" means the abstract; "via review" means the figure was taken from a named review.

  1. WHO 6th-edition reference distributions, reproduced in PMC — primary table. https://pmc.ncbi.nlm.nih.gov/articles/PMC12539902/table/t1/
  2. Boitrelle F et al. Critical review of the WHO 6th edition. Life 2021 — primary. https://pmc.ncbi.nlm.nih.gov/articles/PMC8706130/
  3. Bonde JP et al. Relation between semen quality and fertility: 430 first-pregnancy planners. Lancet 1998 — via review. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(97)10514-1/fulltext
  4. Guzick DS et al. NEJM 2001 — primary. https://www.nejm.org/doi/full/10.1056/NEJMoa003005
  5. Semen parameter thresholds and time-to-conception in 6,061 men. Hum Reprod 2021 — primary. https://academic.oup.com/humrep/article/36/8/2121/6294420
  6. Hamilton JA et al. Total motile sperm count: a better indicator. Hum Reprod 2015 — primary. https://academic.oup.com/humrep/article-lookup/doi/10.1093/humrep/dev058
  7. Keel BA. Within- and between-subject variation. Fertil Steril 2006 — abstract. https://pubmed.ncbi.nlm.nih.gov/16412742/
  8. Misell LM et al. J Urol 2006 — abstract. https://pubmed.ncbi.nlm.nih.gov/16406920/
  9. Abstinence duration and semen parameters: meta-analysis of 13 RCTs. Front Endocrinol 2024 — primary. https://www.frontiersin.org/articles/10.3389/fendo.2024.1373426/full
  10. AUA/ASRM Guideline on Male Infertility (2024 amendment) — primary. https://www.auanet.org/guidelines-and-quality/guidelines/male-infertility
  11. EAU Guidelines: Male Infertility — primary. https://uroweb.org/guidelines/sexual-and-reproductive-health/chapter/male-infertility
  12. Sharma R et al. Smoking and semen quality: meta-analysis. Eur Urol 2016 — abstract. https://pubmed.ncbi.nlm.nih.gov/27113031/
  13. BMI and oligozoospermia/azoospermia: meta-analysis, 9,779 men — primary. https://pmc.ncbi.nlm.nih.gov/articles/PMC5151180/
  14. Garolla A et al. Sauna exposure and sperm parameters. Hum Reprod 2013 — abstract. https://pubmed.ncbi.nlm.nih.gov/23411620/
  15. Agarwal A et al. Varicocelectomy and semen parameters: meta-analysis (figures quoted in PMC) — secondary. https://pmc.ncbi.nlm.nih.gov/articles/PMC4770486/
  16. Persad E et al. Varicocele treatment. Cochrane 2021 — abstract. https://pubmed.ncbi.nlm.nih.gov/33890288/
  17. de Ligny W et al. Antioxidants for male subfertility. Cochrane 2022 — primary. https://pmc.ncbi.nlm.nih.gov/articles/PMC9066298/

Motility and TMSC

Combine volume, concentration and motility into the figure outcome studies actually use.

Read

Morphology

The shape score: subjective, variable between labs, and weak on its own.

Read