What is Oligospermia? Definition, WHO Criteria and a Worked Example

Defining oligospermia in simple terms

Oligospermia is the medical term used when a semen analysis shows a lower than normal concentration of sperm cells in the ejaculate. The word comes from Greek roots meaning “few” and “seed.” It is identified solely by measuring how many sperm are present per millilitre of semen, not by assessing motility or shape.

Clinically, oligospermia matters because sperm concentration is one of the key factors that influence the likelihood of natural conception. A reduced number of sperm lowers the probability that enough viable cells will reach and fertilise an oocyte, although many men with oligospermia still father children.

The condition is usually discovered during a routine fertility work‑up or when a couple experiences difficulty conceiving after regular unprotected intercourse for twelve months or more. A single abnormal result does not confirm a permanent problem; repeat testing is recommended to account for day‑to‑day variation.

World Health Organization reference values

The World Health Organization (WHO) provides reference limits that laboratories use to distinguish normal from low sperm counts. In the WHO Laboratory Manual for the Examination and Processing of Human Semen (5th edition, 2010), the lower reference limit for sperm concentration is 15 million spermatozoa per millilitre.

For the total number of spermatozoa in an ejaculate, the WHO lower reference limit is 39 million. This value is derived by multiplying the reference volume (1.5 mL) by the reference concentration (15 million/mL). Both thresholds are based on data from fertile men and represent the 5th percentile of the distribution.

When a semen analysis yields values below either of these cut‑offs, the result is classified as oligospermia. The WHO also supplies reference ranges for motility (≥ 40 % progressive) and normal morphology (≥ 4 % using strict criteria), but those parameters are separate from the count‑based definition of oligospermia.

Scenario: a 32‑year‑old man seeking fertility assessment

Consider a 32‑year‑old man named Alex who has been trying to conceive with his partner for fourteen months without success. After discussing concerns with his primary care physician, he is referred for a semen analysis to evaluate his sperm production.

Alex receives a collection container and instructions to abstain from ejaculation for two to seven days before providing the sample. He collects the specimen by masturbation in a private room at the clinic, delivers it to the laboratory within thirty minutes, and keeps it at body temperature during transport.

The laboratory measures the semen volume, sperm concentration, motility, and morphology using standardized WHO procedures. The results are entered into a report that will be reviewed by the ordering clinician.

Worked example of the semen analysis results

The laboratory reports the following values for Alex’s sample: semen volume 2.8 mL, sperm concentration 13.0 million spermatozoa per mL, progressive motility 45 %, and normal morphology 4 % (strict criteria). These numbers are typical of what a report might show.

To determine whether Alex meets the WHO criteria for oligospermia, we first calculate the total sperm count in the ejaculate. Total count equals volume multiplied by concentration: 2.8 mL × 13.0 million/mL = 36.4 million spermatozoa.

Next we compare each value to the WHO reference limits. The concentration of 13.0 million/mL is below the 15 million/mL threshold, and the total count of 36.4 million is below the 39 million threshold. Both comparisons indicate a low sperm count.

Interpreting the result against WHO criteria

Because Alex’s sperm concentration is under 15 million/mL, he meets the WHO definition of oligospermia. The total count being under 39 million reinforces the classification. According to further WHO sub‑categories, a concentration between 10 and 15 million/mL is labelled mild oligospermia, 5–10 million/mL moderate, and below 5 million/mL severe.

Alex’s concentration of 13.0 million/mL places him in the mild range. Mild oligospermia often still allows for natural conception, especially if motility and morphology are within normal limits, which in his case they are (45 % motility, 4 % morphology). Nonetheless, the reduced number of sperm lowers the odds per menstrual cycle.

Laboratories usually recommend repeating the analysis after at least four weeks to confirm whether the low count persists, as temporary factors such as illness, heat exposure, or recent medication can affect results.

What the diagnosis means and next steps

A diagnosis of oligospermia does not automatically mean infertility; it is a piece of information that guides further evaluation. Lifestyle factors such as smoking, excessive alcohol, obesity, and exposure to endocrine disruptors can influence sperm production and may be modifiable.

If the low count persists on repeat testing, the clinician may investigate underlying causes, which can include hormonal imbalances, varicocele, genetic conditions, or prior infections. Referral to a urologist or reproductive endocrinologist is appropriate for a comprehensive assessment.

Treatment options vary widely and depend on the identified cause. They may range from lifestyle modifications and medical therapy to assisted reproductive techniques such as intrauterine insemination (IUI) or in‑vitro fertilisation (IVF). Because each case is unique, individuals should discuss their specific situation with a qualified healthcare professional before pursuing any intervention.