Mayo Clinic Health Manager

Get free personalized health guidance for you and your family.

Get Started

Free

E-Newsletter

Subscribe to receive the latest updates on health topics. About our newsletters

  • Housecall
  • Alzheimer's caregiving
  • Living with cancer

Causes

By Mayo Clinic staff

CLICK TO ENLARGE

Illustration of fertilization process Fertilization

The human reproductive process is complex. To become pregnant, the intricate processes of ovulation and fertilization need to work just right.

  • Each month the pituitary gland in a woman's brain sends a signal to her ovaries to prepare an egg for ovulation.
  • The pituitary hormones — follicle-stimulating hormone (FSH) and luteinizing hormone (LH) — stimulate the ovaries to release an egg. This is called ovulation. It is during this time that a woman is fertile (usually about day 14 of a 28-day menstrual cycle).
  • The egg travels through the fallopian tube and can be fertilized within about 24 hours after its release. Conception is more likely to occur when intercourse takes place one to two days prior to ovulation.
  • For pregnancy to occur, a sperm must unite with the egg in the fallopian tube during this time. Sperm are capable of fertilizing the egg for up to 72 hours and must be present in the fallopian tube at the same time as the egg for conception to occur. In order for a sperm to reach an egg, the man must have an erection and ejaculate enough semen to deliver the sperm into the vagina. There must be enough sperm, and it must be the right shape and move in the right way. In addition, the woman must have a healthy vaginal and uterine environment so that the sperm can travel to the egg.
  • If fertilized, the egg moves into the uterus where it attaches to the uterine lining and begins a nine-month process of growth.

For some couples attempting pregnancy, something goes wrong in this complex process, resulting in infertility. The cause or causes of infertility can involve one or both partners:

  • In about 20 percent of cases, infertility is due to a cause involving only the male partner.
  • In about 30 to 40 percent of cases, infertility is due to causes involving both the male and female.
  • In the remaining 40 to 50 percent of cases, infertility is due entirely to a cause involving the female.

Causes of male infertility
A number of things can cause impaired sperm count or mobility, or impaired ability to fertilize the egg. The most common causes of male infertility include abnormal sperm production or function, impaired delivery of sperm, general health and lifestyle issues, and overexposure to certain environmental elements.

Impaired production or function of sperm. Most cases of male infertility are due to problems with the sperm, such as:

  • Impaired shape and movement of sperm. Sperm must be properly shaped and able to move rapidly and accurately 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.
  • Low sperm concentration. 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). A count of 40 million sperm or higher per milliliter of semen indicates increased fertility. Complete failure of the testicles to produce sperm is rare.
  • Varicocele. A varicocele is a varicose 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 from an abnormality affecting the hypothalamus or pituitary gland in the brain that produces the hormones that control the testicles.
  • Genetic defects. In the genetic defect Klinefelter's syndrome, a man has two X chromosomes and one Y chromosome instead of one X and one Y. This causes abnormal development of the testicles, resulting in low or absent sperm production and possibly low testosterone.
  • Infections. Infection may temporarily affect sperm motility. Repeated bouts of 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.

In many instances, no cause for reduced sperm production is found. When sperm concentration is less than 5 million per milliliter of semen, genetic causes could be involved. Genetic testing can reveal whether there are subtle changes in the Y chromosome.

Impaired delivery of sperm. Problems with the delivery of sperm from the penis into the vagina can result in infertility. These may 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. Use of lubricants such as oils or petroleum jelly can be toxic to sperm and impair fertility.
  • 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.
  • Blockage of epididymis or ejaculatory ducts. Some men are born with blockage of the part of the testicle that contains sperm (epididymis) or ejaculatory ducts. Some men lack the tube that carries sperm (vas deferens) from the testicle out to the opening in the penis.
  • 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 complicate the reversal of a vasectomy.
  • 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:

  • 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.
  • Malnutrition. Deficiencies in nutrients such as vitamin C, selenium, zinc and folate may contribute to infertility.
  • Obesity. Increased body mass may be associated with fertility problems in men.
  • Cancer and its treatment. Both radiation and chemotherapy treatment for cancer can impair sperm production, sometimes severely. The closer radiation treatment is to the testicles, the higher the risk of infertility. Removal of one or both testicles due to cancer also may affect male fertility.
  • Alcohol and drugs. Alcohol or drug dependency can be associated with poor health and reduced fertility. The use of certain drugs also can contribute to infertility. Anabolic steroids, for example, which are taken to stimulate muscle strength and growth, can cause the testicles to shrink and sperm production to decrease.
  • Other medical conditions. A severe injury or major surgery can affect male fertility. Certain diseases or conditions, such as diabetes, thyroid disease, Cushing's syndrome, or anemia may be associated with infertility.
  • Age. Men older than age 40 may be less fertile than younger men.

Environmental exposure. Overexposure to certain environmental elements such as heat, toxins and chemicals can reduce sperm count either directly by affecting testicular function or indirectly by altering the male hormonal system. 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 may also cause infertility.
  • Overheating the testicles. Frequent use of saunas or hot tubs can elevate your core body temperature. This may impair your sperm production and lower your sperm count.
  • Substance abuse. 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.

Causes of female infertility
The most common causes of female infertility include fallopian tube damage or blockage, endometriosis, ovulation disorders, elevated prolactin, polycystic ovary syndrome (PCOS), early menopause, benign uterine fibroids and pelvic adhesions.

  • Fallopian tube damage or blockage. Fallopian tube damage usually results from inflammation of the fallopian tube (salpingitis). Chlamydia, a sexually transmitted disease, is the most frequent cause. Tubal inflammation may go unnoticed or may cause pain and fever. Tubal damage may result in a pregnancy in which the fertilized egg is unable to make its way through the fallopian tube to implant in the uterus (ectopic pregnancy). One episode of tubal infection may cause fertility difficulties. The risk of ectopic pregnancy increases with each occurrence of tubal infection.
  • Endometriosis. Endometriosis occurs when the uterine tissue implants and grows outside of the uterus — often affecting the function of the ovaries, uterus and fallopian tubes. These implants respond to the hormonal cycle and grow, shed and bleed in sync with the lining of the uterus each month, which can lead to scarring and inflammation. Pelvic pain and infertility are common in women with endometriosis.
  • Ovulation disorders. Some cases of female infertility are caused by ovulation disorders. Disruption in the part of the brain that regulates ovulation can cause low levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Even slight irregularities in the hormone system can prevent the ovaries from releasing eggs (anovulation). Specific causes of hypothalamic-pituitary disorders that can result in anovulation include injury, tumors, excessive exercise and starvation. In addition, some medications can be associated with ovulation disorders.
  • Elevated prolactin (hyperprolactinemia). The hormone prolactin stimulates breast milk production. High levels in women who aren't pregnant or nursing may affect ovulation. An elevation in prolactin levels may also indicate the presence of a pituitary tumor. In addition, some drugs can elevate levels of prolactin. Milk flow not related to pregnancy or nursing can be a sign of high prolactin.
  • Polycystic ovary syndrome (PCOS). In PCOS, your body produces too much androgen hormone, which affects ovulation. PCOS is also associated with insulin resistance and obesity.
  • Early menopause (premature ovarian failure). Early menopause is the absence of menstruation and the early depletion of ovarian follicles before age 40. Although the cause is often unknown, certain conditions are associated with early menopause, including immune system diseases, radiation or chemotherapy treatment, and smoking.
  • Uterine fibroids. Fibroids are benign tumors in the wall of the uterus and are common in women in their 30s and 40s. Rarely, they may cause infertility by blocking the fallopian tubes. More often, fibroids interfere with proper implantation of the fertilized egg.
  • Pelvic adhesions. Pelvic adhesions are bands of scar tissue that bind organs after pelvic infection, appendicitis, or abdominal or pelvic surgery. This scar tissue formation may impair fertility.

Other causes in women

  • Medications. Temporary infertility may occur with the use of certain medications. In most cases, fertility is restored when the medication is stopped.
  • Thyroid problems. Disorders of the thyroid gland, either too much thyroid hormone (hyperthyroidism) or too little (hypothyroidism), can interrupt the menstrual cycle and cause infertility.
  • Cancer and its treatment. Certain cancers — particularly female reproductive cancers — often severely impair female fertility. Both radiation and chemotherapy may affect a woman's ability to reproduce. Chemotherapy may impair reproductive function and fertility in men and women.
  • Other medical conditions. Medical conditions associated with delayed puberty or amenorrhea, such as Cushing's disease, sickle cell disease, kidney disease and diabetes, can affect a woman's fertility.
  • Caffeine intake. Excessive caffeine consumption can reduce fertility in women.
Risk factors Symptoms
References
  1. Guzick DS. Evaluation of the infertile couple. http://www.uptodate.com/home/index.html. Accessed April 30, 2009.
  2. Hornstein MD et al. Optimizing natural fertility in couples planning pregnancy. http://www.uptodate.com/home/index.html. Accessed April 30, 2009.
  3. Infertility: Frequently asked questions. National Women's Health Information Center. http://www.womenshealth.gov/FAQ/infertility.cfm. Accessed April 30, 2009.
  4. Swerdloff RS, et al. Causes of male infertility. http://www.uptodate.com/home/index.html. Accessed April 30, 2009.
  5. Kuohung W, et al. Etiology of female infertility. http://www.uptodate.com/home/index.html. Accessed April 30, 2009.
  6. Brassard M, et al. Basic infertility including polycystic ovary syndrome. Medical Clinics of North America. 2008;92:1163.
  7. Lobo RA. Infertility: Etiology, diagnostic evaluation, management, prognosis. In: Katz VL, et al., eds. Comprehensive Gynecology. 5th ed. Philadelphia, Pa.: Mosby; 2007. http://www.mdconsult.com/das/book/body/134799312-6/0/1524/267.html?tocnode=53760021&fromURL=267.html#4-u1.0-B978-0-323-02951-3..50044-3_1301. Accessed April 30, 2009.
  8. Kuohung W, et al. Overview of treatment of female infertility. http://www.uptodate.com/home/index.html. Accessed April 30, 2009.
  9. Thinking about fertility treatment. March of dimes. http://www.marchofdimes.com/pnhec/173_14308.asp. Accessed April 30, 2009.
  10. Understanding menopause. U.S. Department of Health and Human Services. http://www.womenshealth.gov/menopause/stages/premature.cfm. Accessed April 30, 2009.
  11. Uterine fibroids: Frequently asked questions. U.S. Department of Health and Human Services. http://www.womenshealth.gov/FAQ/uterine-fibroids.cfm. Accessed April 30, 2009.
  12. Weng X, et al. Maternal caffeine consumption during pregnancy and the risk of miscarriage: A prospective cohort study. American Journal of Obstetrics and Gynecology.2008;198:5.
  13. Sigman M, et al. Male infertility. In: Wein AJ, et al, eds. Campbell-Walsh Urology. 9th ed. Philadelphia, Pa: Saunders Elsevier; 2007. http://www.mdconsult.com/das/book/body/134799312-10/836106647/1445/22.html#4-u1.0-B978-0-7216-0798-6..50021-2_1518. Accessed April 30, 2009.
  14. Casper RF, et al. Ovulation induction with aromatase inhibitors. http://www.uptodate.com/home/index.html. Accessed April 30, 2009.
  15. Hammer LB. Psychiatric aspects of infertility and infertility treatments. Psychiatric Clinics of North America. 2007;30:689.
  16. Domar AD. The impact of acupuncture on in vitro fertilization outcome. Psychiatric Clinics of North America. 2007;30:4.

DS00310

June 27, 2009

© 1998-2009 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.com," "EmbodyHealth," "Reliable tools for healthier lives," "Enhance your life," and the triple-shield Mayo Clinic logo are trademarks of Mayo Foundation for Medical Education and Research.

Print Share Reprints

Text Size: smaller largerlarger