WHO Parameters for Normal Semen Analysis
The World Health Organization establishes the following lower reference limits (fifth centiles) for normal semen analysis: volume ≥1.4 mL, sperm concentration ≥16 million/mL, total sperm number ≥39 million per ejaculate, progressive motility ≥30%, total motility ≥42%, vitality ≥54% live, and morphologically normal forms ≥4.0%. 1
Core Reference Parameters
These WHO reference limits are based on analysis of 3,589 males from 12 countries across 5 continents whose partners achieved pregnancy within 12 months, providing the most robust international standard for semen quality assessment 1. The specific parameters with their 95% confidence intervals are:
- Semen Volume: 1.4 mL (1.3-1.5 mL) 1
- Total Sperm Number: 39 million per ejaculate (35-40 million per ejaculate) 1
- Sperm Concentration: 16 million/mL (15-18 million/mL) 1
- Progressive Motility: 30% (29-31%) 1
- Total Motility: 42% (40-43%) 1
- Vitality: 54% live (50-56%) 1
- Morphologically Normal Forms: 4.0% (3.9-4.0%) 1
- pH: ≥7.0 1
Critical Collection Requirements for Accurate Results
Proper specimen collection is absolutely essential, as improper technique invalidates all results regardless of laboratory quality 1, 2:
- Abstinence period: 2-3 days before collection is mandatory, as inadequate abstinence significantly affects volume and concentration 1, 3, 2
- Transport temperature: Keep specimen at room or body temperature during transport to maintain sample integrity 1, 3
- Analysis timing: Examine within 1 hour of collection for fertility evaluation (or within 2 hours for post-vasectomy analysis) 3
- Collection method: Masturbation or intercourse using specialized semen collection condoms 3, 2
Interpretation Framework: Multi-Parameter Assessment Required
Assessing a combination of several ejaculate parameters is a better predictor of fertility success than any single parameter, with predictive values comparable to diagnostic laboratory tools in other areas of modern clinical medicine. 1 Single-parameter assessments often show discriminatory power close to chance (ROC-AUC near 0.500), making isolated parameter evaluation clinically inadequate 1.
Progressive motility and vitality demonstrate the highest predictive value among standard semen parameters, with the 2010 WHO thresholds showing superior accuracy compared to earlier versions 4.
Number of Analyses Required
- Initial evaluation: Two semen analyses at least one month apart are recommended for initial male infertility evaluation due to significant intra-individual variability 1, 3, 2
- Single analysis utility: Analysis of a single ejaculate is sufficient to determine the most appropriate investigation and treatment pathway, though repeat testing is indicated if abnormalities are found 1
Clinical Context Beyond the Numbers
Semen pH provides critical diagnostic information beyond the standard parameters 1:
- Normal pH (≥7.0): Makes complete distal genital tract obstruction unlikely 1
- Low volume (<1.4 mL) with acidic semen (pH <7.0): Suggests ejaculatory duct obstruction or congenital bilateral absence of the vas deferens 1
Common Pitfalls and Quality Control Issues
The primary cause of semen analysis variability is laboratory failure to adhere to WHO methods, not equipment limitations. 3 Poor adherence to WHO standardized methods is a major problem across andrology laboratories worldwide 3. Critical quality requirements include:
- Use fresh, well-mixed, uncentrifuged samples, as centrifugation interferes with sperm motility assessment 3
- Laboratories should demonstrate documented quality control procedures and achieve ISO 15189 accreditation to WHO standards 3
- Substantial overlap exists in semen parameters between fertile men and those in infertile couples, meaning results cannot definitively determine fertility status 3
Important Clinical Limitations
Semen analysis is only part of the investigation of male fertility potential 1, 3. Other critical attributes include medical history, surgical interventions, sexual function, cryptorchidism, scrotal infections, testosterone/anabolic usage, lifestyle factors, and physical examination findings 1. Even normal semen analysis does not guarantee fertility, as 25% of infertility cases remain unexplained despite normal conventional parameters 2.