A semen analysis is a laboratory test that measures the number, movement, and shape of sperm in a sample of semen, compared against reference values published by the World Health Organization (WHO). The current standard, set out in the WHO laboratory manual's sixth edition (2021), defines the lower reference limits below which a result is flagged for closer attention.1
If you have a results sheet in front of you with numbers and unfamiliar terms, that can feel daunting before anyone has explained what any of it means. This guide walks through each measurement, what the WHO 2021 values are, and — just as importantly — what a result below those values does and does not tell you.
- A semen analysis measures semen volume, sperm concentration, total sperm number, motility (movement), morphology (shape), and vitality.
- The WHO 2021 lower reference limits include a sperm concentration of 16 million per millilitre, total motility of 42%, progressive motility of 30%, and 4% normal forms.
- These limits are the 5th centile of around 3,500 fertile men whose partners conceived naturally within 12 months — a statistical benchmark, not a pass/fail line.
- A single result below a reference value is not a diagnosis of infertility; sperm parameters vary, and a repeat test is usually advised.
- In the UK, a semen analysis is available on the NHS through a GP referral or privately, with an abstinence window of 2–7 days before the sample.
What does a semen analysis measure?
A semen analysis examines a semen sample under a microscope to assess several distinct sperm parameters: how much semen is produced, how many sperm it contains, how well those sperm move, what proportion are normally shaped, and how many are alive. Each parameter reflects a different part of sperm production and function.1
The core measurements are semen volume (millilitres), sperm concentration (million per millilitre), total sperm number (million per ejaculate), total motility and progressive motility (the percentage moving, and the percentage moving forward purposefully), morphology (the percentage with a normal shape), and vitality (the percentage that are alive). Together these build a picture of whether a "male factor" may be contributing to the difficulty you and your partner are facing — which is the case in roughly half of couples seeking help.5
It also helps to know what the test is not. A standard semen analysis counts and describes the sperm in your sample; it does not assess the genetic integrity inside them. That is why some men with results within the reference range still face fertility challenges, and why your specialist may sometimes recommend an additional test such as a sperm DNA fragmentation assessment.1
What are the WHO 2021 reference values for semen analysis?
The WHO 2021 reference values are the lower reference limits for each semen parameter, drawn from the sixth edition of the WHO laboratory manual. A result at or above each limit sits within the reference range; a result below it is flagged. The headline figures are a sperm concentration of 16 million per millilitre and total motility of 42%.1
These limits represent the 5th centile of a reference population of approximately 3,500 fertile men across several countries, all of whose partners had a natural conception with a time-to-pregnancy of 12 months or less.1,3 In other words, 95% of recently fertile men had values at or above these numbers — which is exactly why a result of yours that falls just below one of them is not, on its own, alarming.
| Parameter | WHO 2021 lower reference limit (5th centile) |
|---|---|
| Semen volume | 1.4 mL |
| Sperm concentration | 16 million/mL |
| Total sperm number | 39 million per ejaculate |
| Total motility (progressive + non-progressive) | 42% |
| Progressive motility | 30% |
| Vitality (live sperm) | 54% |
| Normal forms (morphology) | 4% |
You may also see Greek-derived terms on a report. Normozoospermia means all parameters are within the reference range; oligozoospermia means low concentration; asthenozoospermia means reduced motility; teratozoospermia means a low proportion of normal forms; and azoospermia means no sperm were found in the sample.1
What does "below the reference value" actually mean?
A result below a WHO reference value means it sits in the lowest 5% of recently fertile men for that parameter — not that conception is impossible. The reference limits are statistical benchmarks, not diagnostic thresholds, and the WHO manual is explicit that the 5th centile alone is insufficient to diagnose male infertility.1
This matters for how you read your own report, because thresholds are, to a degree, arbitrary lines drawn through a continuous range. When one cohort of men was reassessed using the 2021 criteria, a meaningful proportion who had been classed as "normal" under the older 2010 limits shifted category — illustrating how much weight a single number can carry, and how little a borderline result should be over-interpreted.2
Two principles follow. First, the parameters interact: a sample can be below the limit on one measure yet strong on others, and overall fertility potential depends on the whole picture alongside your partner's fertility. Second, sperm production fluctuates, so one snapshot is rarely the final word. A specialist interprets results in context rather than reading them as a verdict.2,5
How do the WHO 2021 values differ from WHO 2010?
The WHO 2021 values updated the previous 2010 (fifth edition) limits using a larger, refreshed dataset, and the changes were modest in size but meaningful in interpretation. The most-cited shifts are progressive motility (lowered from 32% to 30%) and semen volume (lowered from 1.5 mL to 1.4 mL), while sperm concentration rose slightly from 15 to 16 million per millilitre.1,3
The reference population was expanded by combining the original 2010 data with studies published between 2010 and 2020, giving information on around 3,500 men.3 Because some limits moved up and others moved down, an older report read against the 2010 limits can land in a different category when compared with the 2021 figures — worth knowing if you are looking back at a historical result.
| Parameter | WHO 2010 | WHO 2021 | Direction |
|---|---|---|---|
| Semen volume | 1.5 mL | 1.4 mL | Lower |
| Sperm concentration | 15 million/mL | 16 million/mL | Higher |
| Total sperm number | 39 million | 39 million | Unchanged |
| Total motility | 40% | 42% | Higher |
| Progressive motility | 32% | 30% | Lower |
| Vitality | 58% | 54% | Lower |
| Normal forms | 4% | 4% | Unchanged |
How do you get a semen analysis in the UK?
In the UK, a semen analysis is available either on the NHS following a referral from your GP, or privately through a fertility clinic. NICE advises that couples who have not conceived after a year of regular unprotected intercourse — or sooner if there are known risk factors — should be offered fertility investigations, which include semen analysis for the male partner.6
The NHS route usually begins with a GP appointment; the GP arranges the test through the laboratory's referral system, and you attend an andrology unit to provide a sample. Results are typically sent back to the referring clinician within around 10 working days.9 Private testing can offer shorter waiting times and is an option where NHS access is limited in your area.
Whichever route you take, preparation is the same and it affects the result. Laboratories ask for a period of sexual abstinence of 2–7 days before the sample (around 3–4 days is often considered ideal), as too short or too long an interval can distort the figures. Samples are usually produced by masturbation into a sterile container and kept close to body temperature during transport.
If you are weighing up NHS versus private testing in detail, that comparison deserves its own discussion of cost, turnaround, and what each pathway includes.
What can affect your semen analysis results?
Several everyday factors can temporarily shift a semen analysis result, which is one reason a single test is rarely treated as definitive. The abstinence window, a recent illness or fever, heat exposure, and how the sample was collected and transported can all influence the figures on any given day.1,2
A fever in the roughly two to three months before the test is a common culprit, because sperm take around 74 days to develop — so a sample reflects production from weeks earlier, not just the day you provided it. Testicular heat (from hot baths, saunas, or prolonged laptop use on the lap), high alcohol intake, and smoking are also associated with poorer parameters, while losing part of the sample during collection can artificially lower the volume and count.1,4
Lifestyle is not the whole story — genuine causes such as a low sperm count, a varicocele, hormonal imbalances, or genetic factors exist — but it explains why labs standardise conditions, and why your specialist will often repeat the test before drawing conclusions about your results.5
What are the next steps if your results are below the reference values?
If one or more parameters fall below the WHO 2021 reference values, the usual next step is a repeat semen analysis, typically after an interval of around three months, to confirm whether the finding is consistent or simply a fluctuation.2 A specialist then interprets the combined results alongside your partner's assessment and your wider history.
Depending on the pattern, further investigation may follow. Persistently low concentration can prompt hormone blood tests (such as FSH and testosterone) or, for very low counts, genetic testing; reduced motility or a history of pregnancy loss may lead to a sperm DNA fragmentation test.1,5 Where a treatable cause such as a varicocele is found, addressing it can improve parameters. Lifestyle measures — stopping smoking, moderating alcohol, managing weight, and avoiding excess testicular heat — are first-line steps you can take to support sperm production over a full development cycle.4
Nutrition plays a supporting role too. Reviews of antioxidant and micronutrient supplementation suggest possible improvements in semen parameters in some subfertile men, though the certainty of evidence is limited.7,8 Among micronutrients, zinc contributes to normal fertility and reproduction and selenium contributes to normal spermatogenesis — two reasons these are commonly included in male fertility formulations, including alongside compounds such as L-carnitine. Supplements work best as one part of a broader approach rather than a stand-alone fix.
Frequently Asked Questions
Is a single low semen analysis result a diagnosis of infertility?
No. A single below-reference result is a flag for closer attention, not a diagnosis. Sperm parameters fluctuate with illness, abstinence length, and other factors, so your clinician will usually arrange a repeat test — typically after around three months — before drawing any conclusion.
What is a normal sperm count under WHO 2021?
Under the WHO 2021 reference values, the lower limit for sperm concentration is 16 million per millilitre and for total sperm number is 39 million per ejaculate. A result at or above these sits within the reference range; below is flagged for follow-up.
Why did the WHO change the reference values in 2021?
The 2021 sixth edition updated the limits using a larger, refreshed dataset of around 3,500 fertile men, combining the original 2010 data with studies from 2010 to 2020. Some limits moved slightly up (concentration, total motility) and others slightly down (progressive motility, volume, vitality).
How long should you abstain before a semen analysis?
Most UK laboratories ask for 2–7 days of sexual abstinence before providing a sample, with around 3–4 days often considered ideal. Too short or too long an interval can distort the result, so it is worth checking the specific instructions from your clinic.
Can semen analysis results improve?
They can. Because sperm take roughly 74 days to develop, changes such as stopping smoking, moderating alcohol, avoiding excess heat, and treating an underlying cause like a varicocele may show up in your repeat test after about three months. Improvement is not guaranteed and depends on the cause.
Does a normal semen analysis guarantee fertility?
No. A standard analysis describes sperm quantity, movement, and shape but not their internal genetic quality, so results within the reference range do not rule out a male factor entirely. This is why specialists interpret results in the context of the couple as a whole.
Supporting Your Fertility with FertilitySmart
Understanding your semen analysis is one part of a wider preconception picture, and the nutrients that support normal sperm production — including zinc, which contributes to normal fertility and reproduction, and selenium, which contributes to normal spermatogenesis — feature in many evidence-informed approaches to male reproductive health.
At FertilitySmart, we offer fertility supplements for both women and men formulated with nutrients discussed in this guide. Explore our range of evidence-based fertility supplements to see how nutritional support can fit alongside lifestyle measures and medical advice.
This article is for general information and education and is not medical advice. If your results fall below the reference values, or you are trying to conceive, please speak to your GP or a fertility specialist — and check with them before starting any supplement, particularly if you take medication or have a health condition.
Related Reading
- Male Fertility: The Complete Guide
Our pillar guide to male reproductive health, covering causes, testing, and what can help. - Sperm DNA Fragmentation
What a standard semen analysis misses, and when a DNA integrity test is worth considering. - Low Sperm Count: Causes and Treatment
A deeper look at oligozoospermia, why it happens, and the options. - L-Carnitine for Fertility
The evidence on carnitine and sperm motility. - CoQ10 and Fertility
How CoQ10 relates to sperm energy and oxidative stress. - 4 Common Male Fertility Problems
An overview of the issues most often diagnosed and how they are treated.
References
- World Health Organization. WHO laboratory manual for the examination and processing of human semen. 6th ed. Geneva: World Health Organization; 2021.
- Boeri L, Capogrosso P, Cazzaniga W, et al. The impact of different WHO reference criteria for semen analysis in clinical practice: who will benefit from the new 2021 thresholds for normal semen parameters? Andrology. 2022;10(6):1134-1142. doi:10.1111/andr.13213 doi.org/10.1111/andr.13213
- Campbell MJ, Lotti F, Baldi E, et al. Distribution of semen examination results 2020 — a follow up of data collated for the WHO semen analysis manual 2010. Andrology. 2021;9(3):817-822. doi:10.1111/andr.12983 doi.org/10.1111/andr.12983
- Levine H, Jörgensen N, Martino-Andrade A, et al. Temporal trends in sperm count: a systematic review and meta-regression analysis. Human Reproduction Update. 2017;23(6):646-659.
- Agarwal A, Baskaran S, Parekh N, et al. Male infertility. The Lancet. 2021;397(10271):319-333.
- National Institute for Health and Care Excellence. Fertility problems: assessment and treatment (NG257). London: NICE; 2026.
- de Ligny W, Smits RM, Mackenzie-Proctor R, et al. Antioxidants for male subfertility. Cochrane Database of Systematic Reviews. 2022;5(5):CD007411.
- Salas-Huetos A, Rosique-Esteban N, Becerra-Tomás N, et al. The effect of nutrients and dietary supplements on sperm quality parameters: a systematic review and meta-analysis of randomised clinical trials. Advances in Nutrition. 2018;9(6):833-848.
- NHS. Infertility — diagnosis. National Health Service. nhs.uk/conditions/infertility/diagnosis
Marina Carter
Health & Fertility Writer at FertilitySmart
Marina Carter is FertilitySmart's lead writer on fertility, preconception health, and reproductive nutrition. She translates the clinical and nutritional evidence base into honest, practical guidance for individuals and couples trying to conceive, working closely with the product team to ensure every article reflects current peer-reviewed research and the lived emotional reality of the fertility journey. Read Full Bio →