Male fertility is a complex process. To get your partner pregnant, the following must occur:

  • You must produce healthy sperm. Initially, this involves the growth and formation of the male reproductive organs during puberty. At least one of your testicles must be functioning correctly, and your body must produce testosterone and other hormones to trigger and maintain sperm production.
  • Sperm have to be carried into the semen. Once sperm are produced in the testicles, delicate tubes transport them until they mix with semen and are ejaculated out of the penis.
  • There needs to be enough sperm in the semen. If the number of sperm in your semen (sperm count) is low, it decreases the odds that one of your sperm will fertilize your partner's egg. A low sperm count is fewer than 15 million sperm per milliliter of semen or fewer than 39 million per ejaculate.
  • Sperm must be shaped correctly and able to move. If the movement (motility) or shape (morphology) of your sperm is abnormal, the sperm may not be able to reach or penetrate your partner's egg.

Medical causes

Problems with male fertility can be caused by a number of health issues and medical treatments. Some of these include:

  • Varicocele. A varicocele is a swelling of the veins that drain the testicle. It's a common cause of male infertility. This may prevent normal cooling of the testicle, leading to reduced sperm count and fewer moving sperm.
  • Infection. Some infections can interfere with sperm production or sperm health, or can cause scarring that blocks the passage of sperm. These include some sexually transmitted infections, including chlamydia and gonorrhea; inflammation of the prostate (prostatitis); and inflamed testicles due to mumps (mumps orchitis).
  • Ejaculation issues. Retrograde ejaculation occurs when semen enters the bladder during orgasm instead of emerging out the tip of the penis. Various health conditions can cause retrograde ejaculation, including diabetes, spinal injuries, medications, and surgery of the bladder, prostate or urethra. Some men with spinal cord injuries or certain diseases can't ejaculate semen, even though they still produce sperm.
  • Antibodies that attack sperm. Anti-sperm antibodies are immune system cells that mistakenly identify sperm as harmful invaders and attempt to eliminate them.
  • Tumors. Cancers and nonmalignant tumors can affect the male reproductive organs directly or can affect the glands that release hormones related to reproduction, such as the pituitary gland. In some cases, surgery, radiation or chemotherapy to treat tumors can affect male fertility.
  • Undescended testicles. In some males, during fetal development one or both testicles fail to descend from the abdomen into the sac that normally contains the testicles (scrotum). Decreased fertility is more likely in men who have had this condition.
  • Hormone imbalances. Infertility can result from disorders of the testicles themselves or an abnormality affecting other hormonal systems including the hypothalamus, pituitary, thyroid and adrenal glands. Low testosterone (male hypogonadism) and other hormonal problems have a number of possible underlying causes.
  • Sperm duct defects. The tubes that carry sperm (sperm ducts) can be damaged by illness or injury. Some men experience blockage in the part of the testicle that stores sperm (epididymis) or a blockage of one or both of the tubes that carry sperm out of the testicles. Men with cystic fibrosis and some other inherited conditions may be born without sperm ducts altogether.
  • Chromosome defects. Inherited disorders such as Klinefelter's syndrome — in which a male is born with two X chromosomes and one Y chromosome (instead of one X and one Y) — cause abnormal development of the male reproductive organs. Other genetic syndromes associated with infertility include cystic fibrosis, Kallmann's syndrome, Young's syndrome and Kartagener syndrome.
  • Problems with sexual intercourse. These can include trouble keeping or maintaining an erection sufficient for sex (erectile dysfunction), premature ejaculation, painful intercourse, anatomical abnormalities such as having a urethral opening beneath the penis (hypospadias), or psychological or relationship problems that interfere with sex.
  • Celiac disease. A digestive disorder caused by sensitivity to gluten, celiac disease can cause male infertility. Fertility may improve after adopting a gluten-free diet.
  • Certain medications. Testosterone replacement therapy, long-term anabolic steroid use, cancer medications (chemotherapy), certain antifungal medications, some ulcer drugs and certain other medications can impair sperm production and decrease male fertility.

Environmental causes

Overexposure to certain environmental elements such as heat, toxins and chemicals can reduce sperm production or sperm function. Specific causes include:

  • Industrial chemicals. Extended exposure to benzenes, toluene, xylene, pesticides, herbicides, organic solvents, painting materials and lead may contribute to low sperm counts.
  • Heavy metal exposure. Exposure to lead or other heavy metals also may cause infertility.
  • Radiation or X-rays. Exposure to radiation can reduce sperm production, though it will often eventually return to normal. With high doses of radiation, sperm production can be permanently reduced.
  • Overheating the testicles. Frequent use of saunas or hot tubs may temporarily lower your sperm count. Sitting for long periods, wearing tight clothing or working on a laptop computer for long stretches of time also may increase the temperature in your scrotum and slightly reduce sperm production. The type of underwear you wear is unlikely to make a significant difference in male fertility.

Health, lifestyle and other causes

Some other causes of male infertility include:

  • Illegal drug use. Anabolic steroids taken to stimulate muscle strength and growth can cause the testicles to shrink and sperm production to decrease. Use of cocaine or marijuana may temporarily reduce the number and quality of your sperm as well.
  • Alcohol use. Drinking alcohol can lower testosterone levels, cause erectile dysfunction and decrease sperm production. Liver disease caused by excessive drinking also may lead to fertility problems.
  • Occupation. Certain occupations can increase your risk of infertility, including those associated with extended use of computers or video display monitors, shift work, and work-related stress.
  • Tobacco smoking. Men who smoke may have a lower sperm count than do those who don't smoke. Secondhand smoke also may affect male fertility.
  • Emotional stress. Stress can interfere with certain hormones needed to produce sperm. Severe or prolonged emotional stress, including problems with fertility, can affect your sperm count.
  • Weight. Obesity can cause hormone changes that reduce male fertility.
  • Prolonged bicycling. Prolonged bicycling is another possible cause of reduced fertility due to overheating the testicles. In some cases, bicycle seat pressure on the area behind the testicles (perineum) can cause numbness in the penis and erectile dysfunction.
Sep. 15, 2012