• Oligozoospermia: semen with a low concentration of sperm. It is generally associated with a low sperm production in the testicles, although it is not infrequent to find a partial vas deferens obstruction.
• Asthenozoospermia: reduced sperm progressive motility. It can have its origin in the testicles and the epididymis (the sperm becomes motile here). It could be due to the presence of chemicals, infections, immunological processes in the seminal fluid or genetic abnormalities affecting the sperm structure.
• Teratozoospermia: low percentage of sperm with normal morphology. It can have its origin in the testicles or have a cytogenetical cause. This condition rarely appears alone.

• Oligoasthenoteratozoospermia is the most common alteration on the sperm of infertile men.

The ability of the sperm to fertilize the eggs and achieve a spontaneous pregnancy will depend on the extent of the problem.

Causes of oligoasthenoteratozoospermia:
Testicular failure
Most of oligozoospermias are due to failure of the testicles to make sperm (abnormal spermatogenesis). There are some known factors that may damage the testicles germinal epithelium and reduce the ability to produce sperm: orchitis, trauma, inguinal surgeries, cryptorchidism, chemotherapy, radiotherapy, etc. Sometimes the presence of genetic or chromosomal abnormalities may lead to a poor testicular function, although in most of the cases the cause of a testicular failure is unknown.

Investigations to detect a testicular dysfunction include a blood test to check the FSH and Inhibin B hormone levels. If the blood test does not help to make a diagnosis it is recommended to perform a testicular biopsy to evaluate the extent of the problem and the possibility of treating it with drugs. High FSH levels indicate a testicular disorder without any chances to improve. In these cases it is not possible to use drugs to improve the sperm quality and therefore the only option that may offer higher chances of success is to use assisted conception techniques.

Varicocele: swollen blood vessels around the testicles. A varicocele can be mild, moderate or severe. Varicose veins may cause a rise in testicular temperature or have a toxic effect on the sperm reducing its concentration and motility.  The role of a varicocele in male infertility is controversial and greatly varies from one case to the other.

Inflammation or infection: infections in the testicles, prostate, vas deferens or seminal vesicles may reduce the sperm quality and affect its motility, even if there are no symptoms. Chronic and acute infections can be detected and treated. 

Immunological factor:  in some cases the body does not recognize the own sperm and creates antibodies that attach to the sperm so that they can be detected by the immune system. This may cause the sperm to become immobilized or to clump together affecting its motility and may lead to sperm surface alterations that make it more difficult for sperm to fertilize the eggs.

Hormonal factor: some hormonal disorders, such as the hypogonadotropic hypogonadism, reduce sperm production in the testicles. Treatment involves drugs that help restore normal hormonal levels and recover a good testicle function and a normal sperm production.

Partial blockage: the blockage of one of seminal vesicles results in the semen having sperm cells produced in one single testicle.

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The causes of male infertility are mainly related to the low quality of semen..