Table 2.

Categories of male factor infertility and prevalence: 23% of infertile males have idiopathic causes (Online Resource 1) [5–7, 16, 36–38]

Categories	Definition	Examples of causes	Estimated prevalence N = 8895
Anatomical	Any defect in or within the anatomy that affects mechanical processes that can lead to male infertility	Varicocele, ductal or vasal obstruction, testicular failure, ejaculatory dysfunction, cryptorchidism, testicular torsion, surgical injury, obstructive azoospermia, testicular damage	55%
Genetics and environmental	Genetic abnormalities and/or external biological, chemical and other external factors intertwining to affect processes that can lead to male infertility	Genital infections, drugs, radiation, cancer, systemic disease or infection, immunologic conditions, sickle cell disease, chromosomal aberrations, Sertoli cell syndrome, male accessory gland infection, congenital conditions	17%
Hormonal	Any hormonal imbalance leading to processes affecting sperm production, sexual desire, or any other hormonal process that can lead to male infertility	Hypoandrogenism, decreased or increased hormone levels, psychological factors	4%
Other	Causes stated in studies, so not idiopathic, but provided with minimal information so cannot be accurately categorized	Sexual problems or dysfunction, coital failure, heat atrophy, maturation arrest, ultrastructural	2%
Idiopathic	Abnormal semen analysis with no known cause for that abnormality; broken down by location into males with extracellular sperm defects and general sperm defects	- Extracellular sperm defects: semen volume, semen pH, semen viscosity, sperm agglutination, pyospermia - General sperm defects: oligospermia, azoospermia, asthenozoospermia, teratospermia, necrospermia, hyperspermia	- 23% of infertile males have idiopathic male infertility; 38% of idiopathic males have extracellular sperm defects; 62% of idiopathic males have general sperm defects