Short answer
A semen analysis shows how much semen is produced and how many sperm it contains, how well they swim and what proportion have a normal shape. It is the main first test of male fertility, but a single result is not a diagnosis: counts vary naturally, so an abnormal result is usually repeated. Results below the reference ranges make conception less likely rather than impossible, and results within them do not prove fertility, so interpretation depends on the whole picture for both partners.
Key points
- Reference values come from the WHO (the United Nations health agency) laboratory manual, sixth edition (2021).
- These limits describe the lowest 5% of results in men whose partners conceived within a year.
- Labs usually ask for 2 to 7 days without ejaculation before the test.
- Sperm take roughly two to three months to develop, so a result reflects recent months.
- Incomplete collection is a common cause of a falsely low result.
What is measured
The NHS describes the test as a check for problems such as a low sperm count or sperm that are not moving properly.3 In the laboratory, several features are measured and compared with WHO reference limits.
| Measure | What it means | WHO 2021 lower reference limit |
|---|---|---|
| Semen volume | Amount of fluid in the sample | 1.4 ml1 |
| Sperm concentration | Sperm per millilitre (the “count”) | 16 million per ml1 |
| Total sperm number | Sperm in the whole sample | 39 million1 |
| Progressive motility | Percentage of sperm swimming forward | 30%1 |
| Vitality | Percentage of sperm that are alive | 54%1 |
| Normal forms (morphology) | Percentage with a normal shape | 4%1 |
Some sources use slightly different figures; Mayo Clinic, for example, describes a low sperm count as fewer than 15 million sperm per millilitre, or fewer than 39 million in total.4 Small differences like this are why it is worth asking which reference values a laboratory uses.
How to read the reference values
The reference limits are not a pass or fail line. They are the fifth centile of results from fertile men whose partners became pregnant within 12 months, meaning 95% of those men had higher values.12
A 2021 critical review of the sixth edition notes that it moved away from treating these numbers as thresholds, proposes no decision limits, and that the fifth centile alone is not sufficient to diagnose male infertility.2 Because the limits come from fertile men, a small proportion of fertile men will have values below them. The result has to be read alongside the female partner’s tests and how long the couple have been trying.
Why the test is often repeated
Sperm counts vary naturally from sample to sample, and collection errors are common, so most clinicians check two or more samples over time. Mayo Clinic suggests collecting a second sample at least two weeks after the first.4 One NHS laboratory notes that being asked for a repeat sample is common and not always a cause for concern.5
Sperm take about 42 to 76 days to mature, so a test reflects roughly the previous three months. That also means changes in health or lifestyle take months to show up in results.4
Getting an accurate sample
Laboratories give specific instructions, and following them makes the result more reliable. A typical NHS leaflet asks men not to ejaculate for between 2 and 7 days beforehand, because this affects both the number of sperm and their motility.5 The same leaflet asks for the whole ejaculate to be collected and warns that lubricants can harm sperm.5
Mayo Clinic notes that incomplete or improper collection is one of the most common causes of a low sperm count result.4 If part of the sample is lost, tell the laboratory.
What happens after an abnormal result
If repeat results are abnormal, a clinician may suggest further tests. These can include hormone blood tests, a scrotal ultrasound, a urine test after ejaculation to look for sperm travelling backwards into the bladder, and genetic tests when sperm levels are extremely low.4 A GP may also test for chlamydia and examine the testicles.3
Sperm DNA fragmentation testing is sometimes offered as an extra. The WHO sixth edition introduced it as an extended assessment, but the European Society of Human Reproduction and Embryology (ESHRE) does not currently recommend it for routine clinical use.26
Common questions
Does a normal semen analysis mean there is no male factor?
Not entirely; the reference limits alone cannot diagnose or exclude male infertility.2 Other factors in both partners still need to be considered.
Can lifestyle changes improve results?
Possibly, but any effect takes months to show because of the sperm development cycle.4 A repeat test is usually needed to judge any change.
What if the count is very low?
Further tests are usually advised to look for a cause.4 For background on treatment approaches, see what ICSI is and how IVF and IUI differ.
Is morphology the most important number?
No single number decides it; the WHO review stresses that several criteria are needed for diagnosis.2
Bottom line
A semen analysis describes sperm numbers, movement and shape against reference values drawn from fertile men. It is a starting point rather than a verdict: careful collection, a repeat test and interpretation alongside the female partner’s results give a much clearer picture.
Related reading
- Fertility treatment overview
- What is ICSI?
- IVF vs IUI: what is the difference?
- What does an AMH test tell you?
- Do IVF add-ons work?
Sources
- Andrology Laboratories, Manchester University NHS Foundation Trust. Lower reference limits 2021 (from the WHO laboratory manual for the examination and processing of human semen, sixth edition). https://mft.nhs.uk/app/uploads/sites/4/2023/01/Lower-reference-limits-2021.pdf. Accessed 5 November 2026.
- Boitrelle F, Shah R, Saleh R, Henkel R, Kandil H, Chung E, Vogiatzi P, Zini A, Arafa M, Agarwal A. The sixth edition of the WHO manual for human semen analysis: a critical review and SWOT analysis. Life; 2021;11(12):1368. doi:10.3390/life11121368. https://www.mdpi.com/2075-1729/11/12/1368
- NHS. Infertility: diagnosis. NHS website. https://www.nhs.uk/conditions/infertility/diagnosis/. Accessed 5 November 2026.
- Mayo Clinic. Low sperm count: diagnosis and treatment. Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/diseases-conditions/low-sperm-count/diagnosis-treatment/drc-20374591. Accessed 5 November 2026.
- East Kent Hospitals University NHS Foundation Trust, Andrology Department. Subfertility semen analysis: information for patients who are having fertility tests. https://leaflets.ekhuft.nhs.uk/subfertility-semen-analysis-information-for-patients-who-are-having-fertility-tests/html. Accessed 5 November 2026.
- ESHRE Add-ons Working Group; Lundin K, et al. Good practice recommendations on add-ons in reproductive medicine. Human Reproduction; 2023. doi:10.1093/humrep/dead184. https://discovery.ucl.ac.uk/10178220/1/dead184.pdf
Article history
- — First published.