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Causes of Infertility

There are several common causes of infertility, as well as several subtle causes that are often more difficult to determine. The conditions that cause infertility are equally divided between male factors and female factors. Some couples will be found to have more than one cause of infertility. In about a third of couples, both male and female factors will be found.

Male Factors

Sperm Problems

Approximately half the men who have difficulty achieving pregnancy with their partner will be found to have abnormal sperm on their semen analysis (see below). In the majority of cases, the cause of the abnormality cannot be determined and is presumed to be caused by subtle genetic abnormalities that are difficult or impossible to pinpoint.

Environmental causes – In some cases, reversible sperm problems are related to environmental. Men who wear heavy, tight protective gear for long periods of time (such as fighter pilots or race car drivers) tend to have lower counts, presumably because of the increased temperature to which the testicles are exposed.

Medical causes – In some cases, sperm problems are related to medical causes.

1. Drugs – Some medical conditions and medications can adversely affect sperm counts, and a fertility specialist will advise you about these.

  • Two non-prescription drugs that decrease sperm production are anabolic steroids (testosterone) and marijuana.
  • Many drugs given for chemotherapy will result in temporary or permanent decreases in sperm production.

2. Variocele – A relatively common anatomic cause of semen analysis abnormalities is called a varicocele. This is essentially a varicose vein within the scrotal sac that can decrease sperm number or function by increasing testicular exposure to either heat or blood hormones. Surgical removal has been shown to improve fertility in some men.

Erection and Ejaculation Problems

Diseases and medications can cause men to have difficulty with erection and ejaculation. Diabetes is a common cause of difficulty with both erection and ejaculation. Some medications that treat high blood pressure or depression can cause difficulty with ejaculation.

Female Factors

Ovulation Abnormalities

The most common fertility problems in women are related to ovulation.

Normal Ovulation – The average menstrual cycle is approximately 28 days long, and the first day of menstrual bleeding is called “Day 1” of the cycle. In the average menstrual cycle, ovulation usually occurs on Day 14 of the cycle. As a result, couples who have intercourse between Days 12 and 16 are most likely to achieve pregnancy.

Women who test their urine with an ovulation predictor kit (available over the counter at most pharmacies) usually ovulate the day after detecting an LH surge. In this case, intercourse on the day of ovulation is most likely to result in pregnancy.

Ovulation Problems – Ovulation is controlled by the cyclic interactions of several hormones, and abnormalities in these hormones can prevent normal ovulation. Most women with infrequent or absent menstrual cycles do not ovulate, a condition called anovulation. Even women with very regular cycles can have subtle hormonal abnormalities that decrease the chance of normal ovulation. Common problems that hinder ovulation include:

  • Serious medical conditions
  • Stress
  • Extremes of high or low body weight

Polycystic ovary syndrome (PCOS) – PCOS is a common medical condition characterized by infrequent or absent menses, often accompanied by increased facial hair. Women with this condition usually do not ovulate on a monthly basis. PCOS is more common in heavier women and those with a family history of adult-onset diabetes.

Tubal damage

The fallopian tubes must be healthy in order to pick up the egg, allow it to be fertilized and transport the resulting embryo to the uterus. Any condition that damages the tubes can result in fertility problems.

Infection and Scarring – The most common cause of tubal damage is infection. Pelvic infections or other intra-abdominal infections, such as a ruptured appendix, can result in scar tissue referred to as tubal adhesions. Women infected with Chlamydia are especially prone to tubal damage, even in the absence of clinical symptoms of a pelvic infection. Tubal damage from any cause can also increase the risk of the pregnancy growing in the tube rather than the uterus, a condition referred to as an ectopic pregnancy.

Endometriosis – Another pelvic condition that can decrease fertility is endometriosis. This refers to the growth of cells from the uterine lining (the endometrium) outside of the uterus. These cells are believed to decrease fertility by causing tubal and ovarian scarring or by causing inflammation within the pelvis. This inflammation is believed to alter the hormones and/or the immune processes necessary to achieve pregnancy.

Uterine Abnormalities

Both congenital and acquired uterine abnormalities can decrease the likelihood of achieving pregnancy:

Uterine septum – This refers to an extra stripe of tissue down the middle of the uterus. Women with this problem are more likely to have miscarriages.

Fibroids – The most common uterine abnormality that develops in women is fibroids (uterine leiomyoma). These benign muscle tumors can be found in up to 70% of women and cause symptoms in up to 25%. Fibroids that cause infertility are those located within or adjacent to the uterine cavity or those located anywhere that are >2 ½ inches in diameter. In many cases, it is unclear exactly how fibroids decrease fertility.

Unexplained Infertility

Even after exhaustive testing, no infertility cause can be found in about 10% of patients. Fortunately, most of these problems can be overcome with modern fertility treatments, as discussed below.


  • American Society for Reproductive Medicine. Infertility: an overview, United States. 2003. Birmingham, Ala: American Society for Reproductive Medicine.
  • Falcone T, Hurd WW, eds. Clinical Reproductive Medicine and Surgery, New York: Elsevier, 2007.
  • Hansen JP. Older Maternal Age and Pregnancy Outcome: A Review of the Literature. Obstetrical and Gynecologic Survey 1986;41:726-42.

Prepared in partnership with Melina Dendrinos, MD, Class of 2008

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