Severe Oligospermia Definition
Severe oligospermia is defined as a sperm concentration of less than 5 million sperm per milliliter (<5 × 10⁶/mL). 1
Clinical Threshold and Diagnostic Significance
The WHO-endorsed threshold of <5 million/mL represents the cutoff at which men demonstrate significantly higher rates of chromosomal abnormalities (approximately 4% autosomal abnormalities) compared to fertile populations 1
This specific threshold triggers mandatory genetic testing recommendations, as men below this concentration show substantially elevated risks of karyotype abnormalities and Y-chromosome microdeletions 1, 2
Genetic Testing Requirements at This Threshold
Karyotype analysis should be performed on all males with sperm counts <5 million/mL prior to any therapeutic procedure, including ICSI or testicular sperm extraction 1
Y-chromosome microdeletion testing is mandatory when sperm concentration falls below 1 million/mL, though it is strongly recommended for all men with severe oligospermia (<5 million/mL) 1, 2
The rationale for genetic testing at this threshold includes identifying Klinefelter syndrome (the most common sex chromosomal aneuploidy), translocations, and AZF region deletions that significantly impact prognosis and treatment planning 1
Clinical Implications and Prognosis
Men with severe oligospermia face a 24.6% risk of progressing to azoospermia over time, whereas those with moderate oligospermia (5-15 million/mL) have only a 3.1% risk 3
The reference value of 3-5 million/mL represents the concentration with highest sensitivity (0.746) and specificity (0.711) for predicting progression to azoospermia 3
Sperm cryopreservation should be strongly encouraged for men with counts <5 million/mL due to the substantial risk of future azoospermia 3
Distinction from Other Categories
Moderate oligospermia is typically defined as 5-15 million/mL, while mild oligospermia ranges from 15 million/mL up to the lower reference limit (usually 15-39 million/mL depending on WHO edition) 4, 3
The <5 million/mL threshold specifically correlates with reduced fertilization capacity even with assisted reproductive techniques, though pregnancies remain achievable 5