The sperm is the smallest cell in the human body and likely one of the most extensively studied. The year 2018 saw the publication of the 100,000th scientific paper on this topic. Normal spermatogenesis is highly regulated and reproducible. However, this process, which results in the production of mature male gametes, is subject to congenital or acquired disturbances, often leading to infertility. A male factor is thought to be responsible as the sole or contributing factor in 50% of all couples with infertility. Almost 7% of all men are confronted with fertility problems.1 The pathophysiological factors leading to male-factor infertility are divided into pretesticular, testicular, and posttesticular. Despite all the technological advances and innovation in the diagnosis and evaluation of male infertility, idiopathic etiologies still represent 50% of overall infertility cases.
Spermatogenesis is the process of differentiation and maturation of germ cells.2,3 This process involves mitotic division of spermatogonial stem cells and subsequent meiotic cell division within the seminiferous tubular lumen, supported by the Sertoli cells. Mature spermatozoa—with fertilizing potential—are derived from spermatids through a process of differentiation and maturation called spermiogenesis. This process ensures the production of an average of 300 to 600 sperm per gram of testis per second, an equivalent of millions of sperm per day. The duration of human spermatogenesis is around 70 days, with another few weeks spent in transit through the genital ducts. Spermatogenesis begins at puberty and persists throughout life.
Spermatogenesis (Fig. 3-1) is divided temporally into three main successive stages:
Mitotic cell division that results in multiplication of spermatogonia
Meiotic cell division that leads to reduction of the diploid chromosomes into haploid ones
Spermiogenesis leading to differentiation and maturation of the round spermatids into a spermatozoa
Summary of the most important characteristics of normal spermatogenesis.2,3
Spermatogenesis is a delicate process affected by multiple intrinsic factors, such as hormones, and extrinsic variables, such as ambient temperature and environmental toxins. Clues to the many causes of male-factor infertility will be evident in an abnormal semen analysis. Therefore, the first, and often most revealing, diagnostic evaluation of an infertile man is the semen analysis. The health care provider should be aware of the intrapatient variability of the semen parameters over time. Semen parameters cyclically pass through troughs and peaks multiple times within a given year. For this reason, diagnosing or labeling semen parameters as abnormal should only be done after 2 semen analyses have been performed, separated by several weeks, and after at least 2 to 3 days of abstinence. Occasionally, a third semen analysis may be necessary if the first 2 analyses are discordant. Special attention should be paid to semen volume, sperm concentration, sperm motility, and standardized sperm ...