Male fertility is a complex process that involves many factors, including the release of hormones that trigger the growth of reproductive organs and the production of sperm. To get his partner pregnant, a man must be able to deliver healthy sperm into the vagina that are able to reach, penetrate and fertilize a woman's egg.
• Sperm must be properly shaped and able to move toward the egg for fertilization to occur. If the shape and structure (morphology) of the sperm are abnormal or the movement (motility) is impaired, sperm may not be able to reach or penetrate the egg.
• There has to be enough sperm in the semen to make pregnancy likely. A normal sperm concentration is greater than or equal to 20 million sperm per milliliter of semen. A count of 10 million or fewer sperm per milliliter of semen indicates low sperm concentration (subfertility). Rarely, a man is unable to produce any sperm at all.
Your doctor may use number of tests to try to determine exactly what's causing the problem. In about half the cases of male infertility, an exact cause is never found. But even when the cause isn't entirely clear, treatment may still help. Causes of male fertility include impaired sperm production or function, impaired sperm delivery, lifestyle, and environmental exposure.
Impaired production or function of sperm
A number of specific conditions can cause problems with sperm:
• Varicocele. A varicocele is a swollen vein in the scrotum that may prevent normal cooling of the testicle, leading to reduced sperm count and motility.
• Undescended testicle. Undescended testicle occurs when one or both testicles fail to descend from the abdomen into the scrotum during fetal development. Because the testicles are exposed to the higher internal body temperature, compared with the temperature in the scrotum, sperm production may be affected.
• Testosterone deficiency (male hypogonadism). Infertility can result from disorders of the testicles themselves, or an abnormality affecting the glands in the brain that produce hormones that control the testicles (the hypothalamus or pituitary glands).
• Chromosome defects. Inherited disorders of the testes 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 testicles.
• Infections. Infection may temporarily affect how your sperm moves. Sexually transmitted diseases (STDs), such as chlamydia and gonorrhea, are most often associated with male infertility. These infections can cause scarring and block sperm passage. If mumps, a viral infection usually affecting young children, occurs after puberty, inflammation of the testicles can impair sperm production. Inflammation of the prostate (prostatitis), urethra or epididymis also may alter sperm motility.
• Hormonal disorders. These conditions, such as congenital GnRH deficiency (Kallmann syndrome), affect the release of hormones needed for sexual development or sperm production.
Impaired delivery of sperm
Problems with the delivery of sperm from the penis into the vagina can result in infertility. Examples of problems that can interfere with sperm delivery include:
• Sexual issues. Often treatable, problems with sexual intercourse or technique may affect fertility. Difficulties with erection of the penis (erectile dysfunction), premature ejaculation, painful intercourse (dyspareunia), or psychological or relationship problems can contribute to infertility.
• Blockage of epididymis or vas deferens. Some men are born with blockage of the part of the testicle that stores sperm (epididymis), or have a blockage of the tube that carries sperm (vas deferens) from the testicle out to the penis.
• Retrograde ejaculation. This occurs when semen enters the bladder during orgasm rather than emerging out through the penis. Various conditions can cause retrograde ejaculation, including diabetes, bladder, prostate or urethral surgery, and the use of certain medications.
• No semen (ejaculate). The absence of ejaculate may occur in men with spinal cord injuries or diseases. This fluid carries the sperm from the penis into the vagina.
• Misplaced urinary opening (hypospadias). A birth defect can cause the urinary (urethral) opening to be abnormally located on the underside of the penis. If not surgically corrected, this condition can prevent sperm from reaching the woman's cervix.
• Anti-sperm antibodies. Antibodies that target sperm and weaken or disable them usually occur after surgical blockage of part of the vas deferens for male sterilization (vasectomy). Presence of these antibodies may cause infertility.
• Cystic fibrosis. Men with cystic fibrosis often have a missing or obstructed vas deferens.
General health and lifestyle
A man's general health and lifestyle may affect fertility. Some common causes of infertility related to health and lifestyle include:
• Alcohol and drugs. Alcohol or drug dependency can cause reduced fertility. Anabolic steroids, for example, which are 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.
• 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 may interfere with certain hormones needed to produce sperm. Your sperm count may be affected if you experience excessive or prolonged emotional stress. A problem with fertility itself can sometimes become long term and discouraging, producing more stress. Infertility can affect social relationships and your sex life.
• Other medical conditions. A severe injury, major surgery or cancer can affect male fertility. Certain diseases or conditions, such as kidney disease, cirrhosis, sickle cell anemia and celiac disease can interfere with normal sperm production.
• Age. A gradual decline in fertility is common in men older than 35.
• Malnutrition. Deficiencies in nutrients such as vitamin C, selenium, zinc and folate may contribute to infertility.
• Obesity. Being overweight can cause hormone changes that reduce male fertility.
Overexposure to certain environmental elements such as heat, toxins and chemicals can reduce sperm production or function. Specific causes include:
• Pesticides and other chemicals. Herbicides and insecticides may cause female hormone-like effects in the male body and may be associated with reduced sperm production and testicular cancer. Lead exposure also may cause infertility.
• Overheating the testicles. Frequent use of saunas or hot tubs can temporarily impair your sperm production and lower your sperm count. Sitting for long periods or wearing tight clothing also may increase the temperature in your scrotum and reduce sperm production.
• Exposure to radiation or X-rays. Exposure to radiation can impair sperm production. It can take several years for sperm production to return to normal. With high doses of radiation, sperm production can be permanently impaired.
• Cancer and its treatment. Both radiation and chemotherapy treatment for cancer can impair sperm production. The closer radiation treatment is to the testicles, the higher the risk of infertility.