Key takeaways:
- The WHO 6th Edition semen analysis manual, published in 2021, sets its lower reference limits at the 5th centile of semen results from 3,589 fertile men whose partners conceived naturally within 12 months, which means by design about 1 in 20 of those fertile men fell below each limit (Boitrelle et al., Life, 2021).
- The WHO 6th Edition lists a sperm concentration of 16 million per mL, a total sperm number of 39 million per ejaculate, a total motility of 42%, and 4% normal forms as lower reference limits, and it states that a result under these numbers is not sufficient on its own to diagnose male infertility (Boitrelle et al., Life, 2021).
- A 2022 reappraisal of the 10 studies behind the reference data found that none of the populations was fully described by the pooled limits, so SwimScore treats WHO 6th Edition thresholds as a shared yardstick for reading results rather than a pass or fail line for fertility (Paffoni et al., Human Reproduction, 2022).
Last updated November 3, 2026.
Almost every semen analysis report you will ever see is graded against one document. Your numbers come back, a lab compares them with a set of cutoffs, and some of them get flagged as low. Most men never learn where those cutoffs came from, who they were measured on, or what they were designed to do. That matters, because many men read a flag as a verdict, and the manual behind the flags explicitly says it is not one.
This article explains what the WHO manual is, how its thresholds were set, what changed in the 6th Edition, and where the science is still argued about. It is the foundation for how SwimScore reads your results, so we want you to see both the strengths and the weaknesses.
What Is the WHO Semen Analysis Manual?
The WHO semen analysis manual is the World Health Organization's laboratory handbook for examining and processing human semen, and it is the standard that most labs in the world follow. A semen analysis is a lab test that counts sperm and measures how they move and how they are shaped. The manual tells a lab exactly how to collect a sample, how to count it, how to judge motility (movement) and morphology (shape), and how to report the results so that two labs on opposite sides of the world are measuring the same thing.
The 6th Edition was published in 2021. Its authors also added methods for tests beyond the basic count, including sperm DNA fragmentation, which measures breaks in the genetic material inside sperm, and tests for seminal oxidative stress, a chemical imbalance that can damage sperm. A critical review of the new edition found that these extended tests are well described, although it noted that the manual gives no clinical cutoffs for DNA fragmentation (Boitrelle et al., Life, 2021).
How Does the WHO Set a Lower Reference Limit?
The WHO sets a lower reference limit by measuring semen in a group of men known to be fertile, ranking their results from lowest to highest, and drawing the line at the 5th centile. The 5th centile is the value that 5% of the group falls below. In plain terms, if you take 100 fertile men, about 5 of them will be under the line for any given measure, even though all 100 fathered a child.
The group matters a great deal. For the 6th Edition, the fertile men were those whose partners conceived naturally within 12 months of trying, and the dataset pooled 3,589 men from 12 countries on 5 continents (Boitrelle et al., Life, 2021; Paffoni et al., Human Reproduction, 2022). An accompanying analysis of the data required each sample to come with a sexual abstinence period of 2 to 7 days, because the time since last ejaculation changes the count (Campbell et al., Andrology, 2021). About half of the men came from the earlier 5th Edition dataset of roughly 1,900 men (Cooper et al., Human Reproduction Update, 2010), and the rest were added from newer studies.
This design has one consequence that is easy to miss. The limits describe what is typical for men who conceived quickly. They were not built by comparing fertile men with infertile men and finding the number that best separates them. That is why a result below a limit does not mean you cannot have a child, and a result above it does not guarantee you can.
What Are the WHO 6th Edition Lower Reference Limits?
The WHO 6th Edition lower reference limits are a sperm concentration of 16 million per mL, a total sperm number of 39 million per ejaculate, a total motility of 42%, and 4% normal forms by strict criteria (Paffoni et al., Human Reproduction, 2022; Boitrelle et al., Life, 2021). Concentration is the number of sperm in each milliliter of semen. Total sperm number is the count across the whole ejaculate. Total motility is the share of sperm that move at all. Normal forms, or morphology, is the share with a typical head and tail shape.
The full set reported in the review also includes a semen volume of 1.4 mL (95% confidence interval 1.3 to 1.5) and a progressive motility of 30% (95% confidence interval 29 to 31), where progressive motility means sperm that swim forward in a line or large circles rather than twitching in place (Boitrelle et al., Life, 2021). A confidence interval is the range within which the true value probably sits, given that the study measured a sample of men and not every man.
The numbers moved only slightly from the 5th Edition in 2010, which listed a volume of 1.5 mL, a total motility of 40%, and a progressive motility of 32%, with the same 39 million total count and 4% morphology (Cooper et al., Human Reproduction Update, 2010; Boitrelle et al., Life, 2021). Adding more than 1,700 new men barely shifted the lines, which tells us the limits are fairly stable across datasets.
You will see 32% quoted for progressive motility in many places, including older SwimScore pages. That figure belongs to the 5th Edition. The 6th Edition review reports 30%. The two differ by a couple of percentage points, which is within normal lab and sample variation, but we want you to know both numbers so a report that uses either one does not confuse you.
What Changed in the 6th Edition?
The biggest change in the 6th Edition is a change in language. The editors moved away from calling the 5th centile values "reference limits" that mark normal and abnormal, and said they should be treated as one way of interpreting a result. The manual states that the 5th centile alone is not sufficient to diagnose male infertility, and it talks about replacing fixed thresholds with "decision limits," which would be cutoffs tied to a clinical decision such as choosing a treatment (Boitrelle et al., Life, 2021).
Then comes the awkward part. The review found that the manual proposes no decision limits for basic, extended, or advanced parameters. The authors warned that because nothing replaces the 5th centile values, clinicians will probably keep using them as if they were pass or fail lines (Boitrelle et al., Life, 2021). In practice, that is exactly what happens on most lab reports.
Are the WHO Thresholds Reliable?
The WHO thresholds are reasonable as a common yardstick, but the evidence behind them is weaker than most people assume. A 2022 paper in Human Reproduction examined the 10 studies pooled to create the 6th Edition reference data. It found that most were not designed to set reference values, and that the pooled dataset missed most of the standard requirements for building a reference interval, such as justifying the sample size, reporting how many invited men took part, and handling outliers. When the authors tested each study against the pooled limits, none of the 10 populations was fully described by them, and 88 of 117 comparisons (75%) differed significantly from what was expected (Paffoni et al., Human Reproduction, 2022).
The authors concluded that the studies probably do not come from one population, which might reflect real differences between groups of men or differences in how the labs measured. Either way, the pooled lines are an average of things that do not average neatly. The 6th Edition's own critics also note that South America and Sub-Saharan Africa are underrepresented in the data (Boitrelle et al., Life, 2021).
What We Are More Skeptical About
We are skeptical of any use of the WHO limits as a fertility cutoff. The limits sit at the bottom edge of what fertile men produce, not at the point where fertility fails. Plenty of men below the lines conceive naturally, and plenty of men above them struggle, which is why our article on a normal semen analysis but still not conceiving exists. A report that stamps "abnormal" on a 15 million per mL result and "normal" on a 17 million result is drawing a hard line through a smooth slope.
We are also skeptical of treating a single report as final. Semen results swing from sample to sample, so a value just under or just over a limit says little. Our piece on test-retest variability explains how much, and why repeat testing is part of reading any result well.
Finally, we are cautious about the idea that matching the WHO numbers predicts a pregnancy. Reaching these thresholds has not been shown to guarantee a pregnancy or a live birth, and pregnancy depends on many things beyond sperm, including your partner's age and fertility. The limits tell you where you sit among fertile men. They do not forecast your result.
How Does SwimScore Use the WHO Thresholds?
SwimScore uses the WHO 6th Edition as the common ruler for reading your semen analysis, and it processes every sample in a CLIA-certified lab. CLIA is the federal program that sets quality standards for clinical labs in the United States, and our article on what a CLIA-certified lab is explains why that matters. Using the WHO manual means your sample is counted by the same method used in clinics and research studies, so your results can be compared across labs and over time.
SwimScore does not treat the lines as the end of the story. A concentration of 12 million per mL tells you something different from 2 million, and a motility of 40% sits in a different place than 15%. We look at the pattern across measures. Our article on total motile sperm count shows how count, volume, and motility can be combined into one number that maps better to treatment decisions than any one WHO line does. Our pieces on sperm concentration and sperm morphology go further on how much weight each number deserves.
The WHO manual does not set a cutoff for DNA fragmentation, so SwimScore reports the DNA Fragmentation Index (DFI) separately. DFI is the percentage of sperm with damaged DNA. The ranges we use come from the research on specific lab methods, not from the WHO limits, and our article on whether DNA fragmentation matters explains the evidence and its limits. This is also why a man can have a result inside every WHO limit and still have a high DFI, as we cover in high DNA fragmentation with a normal semen analysis.
How Should You Think About Your Results Practically?
Treat the WHO lines as a map reference, not a grade. Look at where each number sits relative to its limit, how far above or below, and how the numbers look together. A result slightly under one limit with the rest solid is a very different situation from several measures well below, and the first often warrants a repeat test while the second warrants a conversation with a fertility specialist.
Retest before you draw conclusions, using the same lab if you can, and allow at least 12 weeks between tests if you are making a change, since a full cycle of sperm production takes about 72 days. Pair the semen analysis with a hormone panel when the numbers are low, because hormones tell you why a count might be down. If you are curious how a low-count label is named, our guide to oligozoospermia, asthenozoospermia, and teratozoospermia maps each pattern to its clinical term.
Our Take
We know the WHO 6th Edition is the best shared standard the field has for how to run a semen analysis, and that its 5th centile limits describe the lower edge of what fertile men produce. We know the editors themselves say a result under these lines is not enough to diagnose infertility. We also know the data behind the lines is weaker than the confident formatting of a lab report suggests.
What we do not know is where the true dividing line sits between men who will and will not conceive, because the WHO limits were never built to find it. We still think it is worth measuring against them. A common ruler lets you compare your results across labs and across time, spot a pattern that needs follow up, and avoid being falsely reassured or falsely alarmed by a single number. Know your numbers, read them as a set, retest before you act, and bring the full picture to a clinician if anything looks off.
If you want a complete baseline, SwimScore Complete measures sperm concentration, progressive motility, total motility, morphology, DNA Fragmentation Index (DFI), and a hormone panel from home, with every sample processed in a CLIA-certified lab and assessed against WHO 6th Edition thresholds. You can also read more about the research behind SwimScore.
FAQ
What are the WHO 6th Edition semen analysis reference values?
The WHO 6th Edition lists lower reference limits of 16 million sperm per mL, 39 million sperm per ejaculate, 42% total motility, and 4% normal forms, based on the 5th centile of 3,589 fertile men (Paffoni et al., Human Reproduction, 2022; Boitrelle et al., Life, 2021).
What does the 5th centile mean in a semen analysis?
The 5th centile is the value that 5% of a reference group falls below. In the WHO data, about 1 in 20 men whose partners conceived within a year still fell below each limit (Boitrelle et al., Life, 2021).
Does a result below the WHO limit mean I am infertile?
No. The WHO manual states that the 5th centile alone is not sufficient to diagnose male infertility, and men below the limits can and do conceive (Boitrelle et al., Life, 2021).
What changed between the WHO 5th and 6th Edition?
The numbers moved only slightly, for example progressive motility went from 32% to 30% and total motility from 40% to 42%, but the 6th Edition reframed the limits as one interpretation tool and introduced the idea of decision limits without proposing any (Cooper et al., Human Reproduction Update, 2010; Boitrelle et al., Life, 2021).
Are the WHO semen thresholds accurate?
They are a useful common standard, but a 2022 analysis of the 10 studies behind them found that none of the study populations was fully described by the pooled limits, so they should be read as guides and not as sharp cutoffs (Paffoni et al., Human Reproduction, 2022).
References
- Boitrelle F, et al. The Sixth Edition of the WHO Manual for Human Semen Analysis: A Critical Review and SWOT Analysis. Life. 2021. https://pubmed.ncbi.nlm.nih.gov/34947899/
- Paffoni A, et al. The statistical foundation of the reference population for semen analysis included in the sixth edition of the WHO manual: a critical reappraisal of the evidence. Human Reproduction. 2022. https://pubmed.ncbi.nlm.nih.gov/35849333/
- Campbell MJ, et al. Distribution of semen examination results 2020: a follow up of data collated for the WHO semen analysis manual 2010. Andrology. 2021. https://doi.org/10.1111/andr.12983
- Cooper TG, et al. World Health Organization reference values for human semen characteristics. Human Reproduction Update. 2010. https://doi.org/10.1093/humupd/dmp048
Fertility clinics and urology practices: if you want semen analysis and hormone results reported against WHO 6th Edition thresholds in a format your patients can follow, see how SwimScore can support your workflow on our clinic page.
This article is for general education and is not medical advice. Questions about your own semen analysis results should be reviewed with a physician who can interpret them alongside your history and your partner's.
SwimScore uses CLIA-certified labs for all semen analysis and hormone testing, assessed against WHO 6th Edition clinical thresholds.
