Causes of infertility

Other causes of infertility
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.
Combined infertility
In some cases, both the man and woman may be infertile or sub-fertile, and the couple's infertility arises from the combination of these conditions. In other cases, the cause is suspected to be immunological or genetic; it may be that each partner is independently fertile but the couple cannot conceive together without assistance.
Unexplained infertility
Up to 26% of infertile couples have unexplained infertility. In these cases abnormalities are likely to be present but not detected by current methods. Possible problems could be that the egg is not released at the optimum time for fertilization, that it may not enter the fallopian tube, sperm may not be able to reach the egg, fertilization may fail to occur, transport of the zygote may be disturbed, or implantation fails. It is increasingly recognized that egg quality is of critical importance and women of advanced maternal age have eggs of reduced capacity for normal and successful fertilization. Also, polymorphisms in folate pathway genes could be one reason for fertility complications in some women with unexplained infertility.
General health and lifestyle. 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.
• 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.
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.
Environmental and occupational factors
Certain environmental factors may cause men to produce a less concentrated sperm, according to a government report. Exposure to lead, other heavy metals, and pesticides has also 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 cycle (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 PID 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
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, overexercise 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.
• Caffeine intake. Studies are mixed on whether consuming too much caffeine may be associated with decreased fertility. Some studies have shown a decrease in fertility with increased caffeine use while others have not shown adverse effects. If there are effects, it's likely that caffeine has a greater impact on a woman's fertility than on a man's. High caffeine intake does appear to increase the risk of miscarriage.
Age
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 25-30% 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.