The fertility rate in a couple is influenced by several factors. These include: the age of the female partner, age of the male partner, exposure to sexually transmitted disease and to environmental and medical toxins, coexistent disease states, and the specific disorders described below.
While many men with male infertility have oligozoospermia (decrease in number of sperm cells in the ejaculate compared to reference ranges) or azoospermia (no sperm cells in the ejaculate), some infertile men have normal sperm counts. Over 80 percent of men with infertility have low sperm concentrations associated with a decrease in sperm motility (asthenozoospermia) and spermatozoa with normal morphology. Others may have a decrease in sperm motility and abnormal sperm morphology (teratozoospermia).
The causes of male infertility will be reviewed here, with the exception of unexplained infertility. The evaluation and treatment of male infertility and issues related to unexplained infertility are discussed separately. (See "Evaluation of male infertility" and "Treatment of male infertility" and "Unexplained infertility".)
TRENDS IN MALE INFERTILITY
Reports of declining sperm counts and increasing incidence of urogenital abnormalities and testicular cancer in some regions of the world have stirred public interest and concern [1-6]. Whether there is deterioration of semen quality is controversial [7-11]. Later data in fertile men in Europe and the United States show marked differences in sperm concentration between different countries and different regions of the same country [12-14]. The role of environmental pollutants or toxins remains unclear.
Epidemiology studies suggest that fertility rates are lower in men over age 40 [15,16], but results from assisted reproduction techniques have not confirmed this observation [17,18].