The normal reproduction process requires interaction between the female and male reproductive tracts. The woman ovulates and releases an egg from her ovaries to travel through the Fallopian tube to her uterus (womb). The male produces sperm. Both egg and sperm normally meet in the woman's Fallopian tube, where fertilization occurs. The embryo then implants in the uterus for further development.
Infertility occurs when something in this pattern does not happen. The problem could be with the woman (female infertility), with the man (male infertility), or with both. Unknown factors cause infertility 10% of the time. For infertility with an unknown cause, all findings from standard tests may be normal. The actual cause of infertility may not be detected because the problem may be with the egg or sperm itself or with the embryo and its inability to implant.
Pelvic inflammatory disease (PID)
Sexually transmitted diseases, namely, gonorrhea and Chlamydia, may be associated with pelvic inflammatory disease (PID) and damage a woman's Fallopian tubes. A health care professional can detect pelvic inflammatory disease using cultures or molecular biologic studies of vaginal discharge and blood testing for sexually transmitted diseases.
If a woman does not recall ever having pelvic inflammatory disease, her doctor may be able to see scarring or blockage of the tubes during a surgical procedure called laparoscopy. Tiny cameras and instruments are inserted through small cuts in the abdomen to allow the doctor to view the reproductive organs.
Endometriosis affects women during their reproductive years and may contribute to infertility. It can cause pelvic pain and infertility. A woman may be at risk for developing it if she has a family history of the disease. With endometriosis, uterine lining tissue grows outside the uterus and may damage the ovaries and Fallopian tubes. A woman may not know she has a mild form of this condition. Sometimes the doctor finds it during laparoscopy.
Environmental and occupational factors
Certain environmental factors may cause men to produce a less concentrated sperm. Exposure to lead, other heavy metals, and pesticides have been associated with male infertility. Many other factors, such as excessive heat exposure, microwave radiation, ultrasound, and other health hazards, are more controversial as to whether they induce infertility.
Toxic effects related to tobacco, marijuana, and other drugs
Smoking may cause infertility in both men and women. In experimental animals, nicotine has been shown to block the production of sperm and decrease the size of a man's testicles. In women, tobacco changes the cervical mucus, thus affecting the way sperm reach the egg.
Marijuana may disrupt a woman's ovulation (release of the egg). Marijuana use affects men by decreasing the sperm count and the quality of the sperm.
Heroin, cocaine, and crack cocaine use induces similar effects but places the user at increased risk for pelvic inflammatory disease and HIV infection associated with risky sexual behavior.
In women, the effects of alcohol are related more to severe consequences for the fetus. Nevertheless, chronic alcoholism is related to disorders in ovulation and, therefore, interferes with fertility. Alcohol use by men interferes with the synthesis of testosterone and has an impact on sperm concentration. Alcoholism may delay a man's sexual response and may cause impotence (unable to have an erection).
Exercise should be encouraged as part of normal activities. However, too much exercise is dangerous, especially for long-distance runners. For women, it may result in disruption of the ovulation cycle, cause no menstrual periods, or result in miscarriages (loss of pregnancy). In men, excessive exercise may cause a low sperm count.
Inadequate diet associated with extreme weight loss or gain
Obesity is becoming a major health issue in the United States. Obesity has an impact on infertility only when a woman's weight reaches extremes.
Weight loss with anorexia or bulimia can create problems with menstrual periods (no periods) and thyroid levels, thus disrupting normal ovulation.
A woman becomes less fertile as she ages into her fifth decade of life (age 40-49 years). Among men, as they age, levels of testosterone fall, and the volume and concentration of sperm change.
Healthy couples younger than 30 years who have regular sexual intercourse and use no birth control methods have a 25% to 30% chance of achieving pregnancy each month. A woman's peak fertility is early in the third decade of life. As a woman ages beyond 35 years (and particularly after age 40 years), the likelihood of becoming pregnant is less than 10% per month.
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"Infertility." American Pregnancy Association.
"FastStats: Infertility." CDC.gov.