Human sperm are created in the testis via a highly regulated and complex hormonal pathway arising from the hypothalamic–pituitary–testicular (HPT) axis under complex paracrine control by growth factors and cytokines. Following their creation, sperm must travel through the seminiferous tubules, epididymis, vas deferens, ejaculatory ducts, and urethra until they are expelled through ejaculation into the female genital tract. Fertilization capabilities of the sperm require morphologic and molecular changes that are acquired during transit of sperm through the male and female reproductive tracts.

Routine semen analysis remains the one laboratory diagnostic test that should be the cornerstone of evaluation of the infertile male. With visual assessment of semen characteristics, namely, color, volume (also may be defined by weight, as recommended by the World Health Organization (WHO) [1]), viscosity, and liquefaction, the analysis proceeds with a strictly defined series of steps using microscopic assessment of sperm agglutination, sperm aggregation, motility, morphology, and sperm concentration. The test provides a wealth of information about spermatogenesis (sperm morphology and count), function of the testis, and the genitourinary tract and glands – production of normal-appearing spermatozoa, acquisition of sperm motility during passage through the epididymis, functions of accessory organs (seminal vesicles and prostate impacting semen volume, liquefaction), including a reflection of androgen action in these tissues/organs, patency and health of the genital tract, and processes of emission and ejaculation. Yet, with few exceptions (no sperm in the ejaculate, complete globozoospermia, or asthenozoospermia), the test cannot be used to distinguish fertile from infertile men [2]. Even in the presence of severe idiopathic oligozoospermia, paternity has been documented without the use of assisted reproductive technology (ART) [3], and studies of large numbers of proven fertile men undergoing vasectomy revealed that about 11 percent of them were severely oligozoospermic who nevertheless fathered children without medical assistance (based upon WHO 3 and WHO 4 criteria; reviewed in [4]). Indeed, although increasing numbers of abnormal semen parameters are associated with a higher risk of infertility in men, for an individual male, it is impossible to predict with certainty whether or not he is infertile, based upon abnormal semen parameters.

The last and fourth edition of Infertility in the Male was published in 2009, and significant advances were realized in reproductive medicine and surgery in the intervening decade. In this edition, we have covered the more recent advances in the field while maintaining the core foundation of information needed for practitioners in diagnosing and treating the man seeking care for fertility. We have also endeavored to make the book more structured, and hopefully easier to use, for the student and specialist alike.