In 1999, the World Health Organization (WHO) recommended the classification of male infertility (16 categories): 1, sexual dysfunctional infertility; 2, immune infertility; 3, simple abnormal seminal plasma infertility; 4, medical factors of infertility; 5, systemic disease infertility; 6, congenital factors of infertility; 7, acquired testicular damage infertility; 8, varicocele infertility; 9, male gonadal infection Infertility; 10, endocrine infertility; 11, idiopathic oligospermia; 12, idiopathic weak sperm; 13, idiopathic aberrant sperm; 14, obstructive azoospermia; 15, idiopathic azoospermia; 16, unexplained infertility.