WHO 6th edition (2021) lower reference limits: semen volume 1.4 mL, concentration 16 million/mL, total sperm number 39 million, progressive motility 30%, normal forms 4%. WHO states these do not represent a limit between fertile and infertile men.
Sperm morphology: what the percentage means
Morphology is the proportion of sperm with a normal shape. It causes more unnecessary alarm than any other semen parameter, largely because the number looks frightening without context.
The reference value
Under the WHO laboratory manual, sixth edition (2021), the lower fifth percentile for normal forms is 4%.
Yes — four percent. A man whose sample shows 4% normally shaped sperm sits at the bottom of the range seen in men who conceived naturally within a year. Human sperm are morphologically variable in a way that is normal for the species.
What that number actually is, and is not
This is the part that matters more than the figure itself. WHO states plainly:
> "The lower fifth percentile of data from men in the reference population does not represent a limit between fertile and infertile men."
The manual also notes it "is not a guideline for clinical decisions", and that there is substantial overlap in semen results between fertile and infertile men.
So this is not a pass mark. It describes where 95% of men who conceived naturally within a year fell. Men below it conceive; men above it sometimes do not.
The full reference set (WHO 6th edition, lower 5th percentile)
| Parameter | Value |
|---|---|
| Semen volume | 1.4 mL |
| Sperm concentration | 16 million/mL |
| Total sperm number | 39 million per ejaculate |
| Total motility | 42% |
| Progressive motility | 30% |
| Vitality | 54% |
| Normal forms | 4% |
Check which edition your laboratory used. The 5th edition (2010) figures differ — semen volume was 1.5 mL, concentration 15 million/mL — and many laboratories and websites still quote them.
Total number matters more than concentration
WHO notes that total sperm number per ejaculate has more diagnostic value than concentration — but only if semen volume is measured accurately. If your report gives concentration without total number, ask for it.
One number tells you little
The AUA/ASRM guideline notes that results are of greatest clinical significance when multiple abnormalities are present. With the exception of azoospermia, complete globozoospermia, necrozoospermia and complete asthenozoospermia, no single parameter is highly predictive of fertility on its own.
Repeat before concluding
Parameters vary substantially between samples from the same man. Abstinence of two to seven days, complete collection including the first portion, and prompt delivery to the laboratory all affect the result.
Have the whole report interpreted by a urologist or andrologist rather than reacting to one figure.
Sources
- AUA/ASRM — Diagnosis and treatment of infertility in men (2021)
- WHO laboratory manual for the examination and processing of human semen, 6th edition (2021)
- WHO laboratory manual for the examination and processing of human semen, 6th edition (2021)
Frequently Asked Questions
What is a normal sperm morphology percentage?▾
Per WHO 2021 Kruger strict criteria, ≥4% normal forms is the lower reference limit. Most fertile men have 8–15% normal forms. Values of 4–7% are borderline; below 4% is teratospermia. Isolated teratospermia with normal count and motility rarely prevents natural conception.
Can poor sperm morphology cause miscarriage?▾
Very poor morphology is associated with higher DNA fragmentation — which in turn is associated with increased miscarriage risk. Isolated teratospermia is not a major independent cause of miscarriage. If you have recurrent miscarriage with poor morphology, a sperm DNA fragmentation (DFI) test is more informative than morphology alone.
Does ICSI bypass morphology problems?▾
Yes — ICSI (Intracytoplasmic Sperm Injection) injects a single sperm directly into each egg, bypassing the need for normal morphology to penetrate the egg coat. ICSI achieves comparable fertilisation rates regardless of morphology severity, provided live sperm are present. It is the standard approach for severe teratospermia or specific acrosomal defects.