Causes of Male Infertility

Around 90% of male infertility is related to poor sperm quality, low sperm count, or both. The other 10% of cases are caused by hormonal factors, anatomical problems, and genetic defects.


Sperm Abnormalities

Sperm abnormalities are caused by chemical exposure, congenital birth defects, and certain lifestyle habits. Sperm abnormalities are not known in many cases. These abnormalities include:

  • Poor sperm motility (asthenospermia) – The sperm’s ability to move is called motility. When movement is not in a straight line, or the sperm moves slow, the sperm cannot penetrate the cervical mucus or the hard outer shell (zona pellucida) of the egg.
  • Low sperm count (oligospermia) – When the sperm count is less than 20 million per milliliter, it is considered a low sperm count. Azoospermia is the complete absence of any sperm cells in the ejaculate. Obstruction anywhere along the male reproductive tract will cause reduced sperm counts.
  • Abnormal sperm morphology (teratospermia) – The morphology of sperm refers to its shape and structure. Abnormally shaped sperm are incapable of fertilizing the egg. Around 60% of sperm must be normal for adequate fertilization.


Structural Abnormalities

Any structural abnormalities can block the testes, tubes, or other reproductive structures and damage the reproductive tract. These include:

  • Retrograde ejaculation – This occurs when the bladder muscles do not work properly during orgasm. This forces the sperm backward and into the bladder, which impairs sperm count and quality. Retrograde ejaculation can be caused by multiple sclerosis, diabetes, spinal cord injury, surgery to the prostate or bladder, and aging.
  • Cryptorchidism – Usually seen in newborns, this condition is where the testicles fail to descent from the abdomen to the scrotum.
  • Hypospadias – With this birth defect, the urinary opening forms on the underside of the penis instead of the top. This condition prevents the sperm from reaching the cervix.
  • Blockage of the reproductive tract – Blockage in the ejaculatory ducts or epididymis will later affect fertility. Some men are born without a vas deferens, which is the tube that carries semen from the testicles and out the penis.


Hormonal Deficiencies

Hypogonadism is the medical term for severe deficiency of gonadotropin-releasing hormone (GnRH), which is the hormone that signals the release of testosterone and other reproductive hormones. Low levels of testosterone can cause defective sperm production. Hypogonadism is often the result of uncommon genetic diseases that affect the pituitary gland, such Kallman syndrome, panhypopituitarism, and FSH or LH deficiencies.


Genetic Disorders

Certain inherited disorders impair fertility. These include:

  • Cystic fibrosis can cause obstructed or missing vas deferens (tubes that transport sperm).
  • Polycystic kidney disease causes large cysts on the kidneys and other organs, which leads to infertility.
  • Kartagener syndrome is a rare condition that impairs sperm motility.
  • Klinefelter syndrome is marked by one Y and two X chromosomes, which causes low testosterone levels.



An abnormally enlarged or twisted varicose vein in the spermatic cord is called a varicocele. Found in around 15% of men, varicoceles contribute to 40% of infertility. These structures raise the testicular temperature, which affects sperm movement, production, and shape.


Lifestyle Factors

Nearly any major mental or physical stress can reduce the sperm count and quality. Common conditions that affect sperm include:

  • Sexually transmitted infections – Repeated gonorrhea or chlamydia infections are associated with male infertility. These infections scar the reproductive tract and block sperm passage.
  • Substance abuse – Any substance can alter the number and quality of sperm. Chemicals also impair the sperm ability to penetrate the egg or swim in a straight line.
  • Bicycling – Riding a bicycle for a long time can affect erectile function. In addition, pressure from the seat damages the nerves and blood vessels responsible for erections.