Presence of abnormal semen parameters in the male partner of a couple unable to achieve conception after 1 year of unprotected intercourse.
Male factor alone contributes to 20% of cases of infertile couples and to an additional 30% to 40% in combination with other factors.
Most cases are of unknown aetiology.
Diagnosed if abnormal semen parameters in 2 semen analyses separated by 1 month.
Sperm functional assays, endocrine tests, genetic testing, and imaging can be helpful.
Treatment should be targeted to the aetiological factors whenever possible.
Assisted reproductive techniques are often the fastest and most effective method to achieve pregnancy regardless of the aetiology.
The clinical definition of male factor infertility is the presence of abnormal semen parameters in the male partner of a couple unable to achieve conception after 1 year of unprotected intercourse. The World Health Organization defines male factor infertility as the presence of ≥1 abnormalities in the semen analysis or the presence of inadequate sexual or ejaculatory function. 
Director of Male Reproductive Medicine and Sexual Medicine
Henry Ford Health System
K9 Urology Clinic
AAD declares that he has no competing interests.
IVF Michigan Fertility Center
AOH declares that he has no competing interests.
Dr Ali A. Dabaja and Dr Ahmad O. Hammoud would like to gratefully acknowledge Dr Benjamin Emery, the previous contributor to this monograph. BE declares that he has no competing interests.
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