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 "Ev