WHO 2021 Semen Analysis Reference Limits
The WHO 2021 manual provides lower reference limits derived from the
5th percentile of a fertile population. These are not “normal versus abnormal” cutoffs in a simple sense; they represent the value below which only
5% of men who achieved a pregnancy fall. A result below a limit means the parameter is in the lowest 5th percentile of fertile men, which raises concern but does not by itself diagnose infertility.
The husband’s values are compared with the WHO 2021 lower reference limits as follows:
| Parameter | WHO 2021 Lower Reference Limit | Husband’s Result | Interpretation |
|---|
| Volume | 1.4 mL | 2.8 mL | Above limit |
| Sperm concentration | 16 million/mL | 18 million/mL | Above limit |
| Total sperm number | 39 million per ejaculate | 50 million per ejaculate | Above limit |
| Progressive motility | 30% | 21% | Below limit |
| Normal forms (strict criteria) | 4% | 5% | Above limit |
| Vitality (live sperm) | 54% | 68% | Above limit |
Only
progressive motility falls below the reference limit. The correct answer is therefore
1. Progressive motility.
Why Progressive Motility Matters
Progressive motility refers to sperm that move forward in a straight line or in large circles, as opposed to non-progressive motility (twitching or small circles in place) or immotility. Forward movement is essential for the sperm to travel through the cervical mucus, traverse the uterus, and reach the ampulla of the fallopian tube where fertilization occurs.
A progressive motility below 30% suggests that fewer sperm are capable of making this journey, which can reduce the probability of natural conception.
It is important to separate motility from vitality.
Vitality measures the proportion of sperm that are alive, regardless of whether they move. A man can have a normal vitality but low progressive motility, meaning the sperm are alive but not swimming effectively. In this case, vitality is
68%, well above the WHO limit of
54%, so the low motility is not simply due to a high proportion of dead sperm. The problem is functional movement, not viability.
Clinical Interpretation and the Role of Repeated Testing
A single semen analysis with one abnormal parameter does not establish male infertility. Semen parameters fluctuate significantly over time due to transient factors such as febrile illness, stress, recent ejaculation frequency, medications, and laboratory variation.
When one parameter is below the reference limit, the WHO recommends repeating the semen analysis after an appropriate interval, typically 2 to 3 months, which reflects the duration of a full spermatogenic cycle.
The 2021 WHO manual and the supporting distribution data emphasize that reference limits are derived from fertile men, not from a clean separation between fertile and infertile populations.
Watch out! A value above the lower reference limit does not guarantee fertility, and a value below it does not prove infertility. The limits are screening tools that guide further evaluation.
In this scenario, the husband’s specimen was collected after
3 days of abstinence. The WHO recommends
2 to 7 days of abstinence before collection. Shorter abstinence can lower semen volume and sperm concentration, while longer abstinence can reduce motility and increase the proportion of dead sperm. The
3-day abstinence falls within the recommended window, so the low progressive motility cannot be attributed to an inappropriate abstinence period. This strengthens the need to repeat the test and evaluate the couple comprehensively.
Nursing Considerations in the Infertility Clinic
When teaching a couple about semen analysis results, the nurse should explain that the report is interpreted as a whole, not parameter by parameter in isolation.
The most clinically informative combination is total sperm number, progressive motility, and normal morphology, because these three parameters together reflect the sperm’s ability to reach and fertilize the oocyte. In this case, total sperm number and morphology are acceptable, but progressive motility is impaired, which may warrant referral for further andrological evaluation, including assessment for varicocele, hormonal status, or lifestyle factors such as smoking, alcohol, or occupational heat exposure.
The nurse should also provide clear instructions for repeat collection: maintain
2 to 7 days of abstinence, collect the entire ejaculate into a sterile container, deliver the specimen to the laboratory within
1 hour while keeping it at body temperature, and report any recent febrile illness or medication use. These measures reduce pre-analytical error and improve the reliability of the repeat analysis.