Most causes of male infertility are related to the presence of too few sperm to fertilize an egg or to abnormal sperm shape or motility (the vigor with which sperm cells propel themselves) (American Society for Reproductive Medicine, 2008). A major cause of infer­tility in men is a damaged or enlarged vein in the testis or vas deferens, called a varicocele (Abdel-Meguid, 2012; Zohdy et al., 2011). The varicocele causes blood to pool in the scrotum, which elevates temperature in the area, impairing sperm production (Mishail et al., 2009). Infectious diseases of the male reproductive tract can alter sperm production, viability, and transport. For instance, mumps, when it occurs in adulthood, can affect the testes, lowering sperm output, and infection of the vas deferens can block the passage of sperm. Infections caused by STIs are another major cause of infertility. Smoking, alcohol, and drug use and abuse reduce fertility as well (Springen, 2008). Cocaine use decreases spermatogenesis, and marijuana impedes sperm motility. Environmental toxins, such as chemicals, pollutants, and radiation, can also produce low sperm counts and abnormal sperm cells. Sperm absorb and metabolize environmental toxins more easily than do other body cells, which can also result in birth defects. Environmental factors are the likely cause for the worldwide drop in sperm counts in the last 50 years (Joensen et al., 2009).

To improve the quality of sperm, research indicates that ejaculating daily is helpful (Henderson, 2007). In contrast, when the sperm count is low, to increase the concentra­tion of sperm, the optimal frequency of ejaculation during intercourse is usually every other day, beginning 6 days before ovulation and during the week that the woman is ovulating. A man with a low sperm count might also want to avoid taking hot baths, wearing tight clothing and undershorts, and riding bicycles long distances, because these and similar environments subject the testes to higher than normal temperatures.

For poor semen quality or quantity, intracytoplasmic sperm injection (ICSI) can result in pregnancy. ICSI involves injecting each harvested egg with a single sperm and is one of the advances in reproductive technology we discuss in the next section.