Causes:

More than 90% of male infertility cases are due to low sperm counts, poor sperm quality, or both. The remaining cases of male infertility can be caused by a number of factors including anatomical problems, hormonal imbalances, and genetic defects.

Sperm Abnormalities

Sperm abnormalities can be caused by a range of factors, including congenital birth defects, disease, chemical exposure, and lifestyle habits. (See "Risk Factors" section.) In many cases, the causes of sperm abnormalities are unknown.

Sperm abnormalities are categorized by whether they affect sperm count, sperm movement, or sperm shape. They include:

• Low Sperm Count (Oligospermia). A sperm count of less than 20 million/mL is considered low sperm. Azoospermia refers to the complete absence of sperm cells in the ejaculate, and accounts for 10 - 15% of cases of male infertility. Partial obstruction anywhere in the long passages through which sperm pass can reduce sperm counts. Sperm count varies widely over time, and temporary low counts are common. Therefore, a single test that reports a low count may not be a representative result.
• Poor Sperm Motility (Asthenospermia). Sperm motility is the sperm's ability to move. If movement is slow, not in a straight line, or both, the sperm have difficulty invading the cervical mucous or penetrating the hard outer shell of the egg. If 60% or more of sperm have normal motility, the sperm is at least average in quality. If less than 40% of sperm are able to move in a straight line, the condition is considered abnormal. Sperm that move sluggishly may have genetic or other defects that render them incapable of fertilizing the egg. Poor sperm motility may be associated with DNA fragmentation and may increase the risk for passing on genetic diseases.
• Abnormal Sperm Morphology (Teratospermia). Morphology refers to shape and structure. Abnormally shaped sperm cannot fertilize an egg. About 60% of the sperm should be normal in size and shape for adequate fertility. The perfect sperm structure is an oval head and long tail.

Retrograde Ejaculation

Retrograde ejaculation occurs when the muscles of the bladder wall do not function properly during orgasm and sperm are forced backward into the bladder instead of forward out of the urethra. Sperm quality is often impaired.

Retrograde ejaculation can be the consequence of several conditions:

• Surgery to the lower part of the bladder or prostate (the most common cause of retrograde ejaculation)
• Diseases such as diabetes and multiple sclerosis
• Spinal cord injury or surgery
• Medications such as tranquilizers, certain antipsychotics, or blood pressure medications also may cause temporary retrograde ejaculation.
• Aging

Structural Abnormalities

Any structural abnormalities that damage or block the testes, tubes, or other reproductive structures can have a profound effect on fertility.

Cryptorchidism. Cryptorchidism is a condition usually seen in newborn infants in which the testicles fail to descend from the abdomen into the scrotum. Cryptorchidism is associated with mild to severe impairment of sperm production.

Hypospadias. This is a birth defect in which the urinary opening is on the underside of the penis, can prevent sperm from reaching the cervix if not surgically corrected.

Blockage in the Tubes that Transport Sperm. Some men are born with a blockage in the epididymis or ejaculatory ducts or other problems that later affect fertility. Some men lack the vas deferens, the tube that carries sperm from the testicles out through the penis. Low semen levels in ejaculate may be associated with structural abnormalities in the tubes transporting the sperm. (A normal amount of semen is 2.5 - 5 mL, or about 1/2 - 1 teaspoon.)

Hormonal Deficiencies

Hypogonadism is the general name for a severe deficiency in gonadotropin-releasing hormone (GnRH), the primary hormone that signals the process leading to the release of testosterone and other important reproductive hormones. Low levels of testosterone from any cause may result in defective sperm production.

Hypogonadism is uncommon and is most often present at the time of birth, usually the result of rare genetic diseases affecting the pituitary gland that may include selective deficiencies of the hormones FSH and LH, Kallman syndrome, or panhypopituitarism, in which the pituitary gland fails to make almost all hormones. It can also develop later in life from brain or pituitary gland tumors or as a result of radiation treatments.

Genetic Disorders

Certain inherited disorders can impair fertility. Examples include:

• Cystic fibrosis can cause missing or obstructed vas deferens (the tubes that carry sperm).
• Polycystic kidney disease, a relatively common genetic disorder that causes large cysts to form on the kidneys and other organs during adulthood, may cause infertility as the first symptom if cysts develop in the reproductive tract.
• Klinefelter syndrome is marked by two X and one Y chromosomes (the norm is one X and one Y), which leads to the destruction of the lining of the seminiferous tubules in the testicles during puberty, although most other male physical attributes are unimpaired.
• Kartagener syndrome, a rare disorder that is associated with a reversed position of the major organs, also causes impaired sperm motility.