Causes of Infertility in Women
Several factors have been associated with an increased risk for infertility, including being 35 years of age or older, a history of pelvic inflammatory disease, and various lifestyle behaviors. There has been speculation that exposure to certain environmental toxins may cause infertility, but the relationship has not been proven.
Conception cannot happen without ovulation. The absence of ovulation, anovulation, may be affected by the factors mentioned above, but its most common cause is polycystic ovary syndrome. Abnormal levels of prolactin (PRL) or thyroid-stimulating hormone (TSH) can also cause anovulation.
Another cause for anovulation is hypothalamic ammenorrhea, which often is seen in very thin women, especially those who exercise excessively. This manifestation often occurs in Olympic development athletes.
The proportion of the female population that is infertile increases with age. In one study, for example, less than 5% of women under the age of 20, 10% of the women between the ages of 20 and 30, and 15% of those between the ages of 30 and 35 were infertile. Fertility dropped dramatically around the age of 35, and as many as 25% to 30% of women older than 35 were infertile.
Why does infertility increase with age? Because fecundity, or the ability to conceive, naturally decreases over time as part of the normal aging process. The early egg cell (called an oocyte) ages quickly. Women normally lose about 1000 eggs every month. Losing more than 1000 eggs every month may contribute to ovarian failure. Also, there are a variety of diseases, such as endometriosis and certain sexually transmitted diseases (STDs), that may worsen over time and eventually lead to infertility, meaning that the older a person gets the more likely infertility will develop if he or she has one of these underlying conditions.
Pelvic inflammatory disease (PID) is a very serious pelvic inflammation that results from untreated vaginal or cervical infections, most commonly chlamydia and gonorrhea. If left untreated, bacteria make their way up through the uterus and into the fallopian tubes, ovaries, and surrounding tissues. PID does serious damage to the reproductive tract, often scarring and blocking the fallopian tubes. Scarring prevents fertilization from ever occurring.
PID is one of the major causes of infertility among women of reproductive age. In one study, for example, 21% of the women with PID were infertile compared to only 3% of the women without PID. And the more episodes of PID a woman experiences, the greater her risk for infertility. However, after PID treatment, pregnancy often can be achieved through IVF.
Because PID results from untreated sexually transmitted infections, lifestyle choices that increase the likelihood that a woman will become infected with an STD also increase her chances of PID-induced infertility. These include not using a latex barrier (a condom or other form of STD protection) to prevent the transmission of STDs, as well as having multiple sex partners.
In addition to sexual behavior, other behaviors have been shown to be associated with an increased likelihood of infertility:
- Smoking: Although much of the evidence is controversial, at least one major study shows a significant increase in infertility among people who smoke at least one pack of cigarettes a day and in smokers who started using tobacco before the age of 18. (See also: women and smoking, smoking cessation)
The reasons that smoking contributes to male and female infertility are twofold: 1) Cigarette smoke constricts blood vessels (vasoconstriction), reducing blood flow to the ovaries, endometrial lining, and testes. 2) Toxins in cigarettes can contribute to cell damage in the ovaries and testes.
- Alcohol: Scientists are not sure how alcohol affects fertility, but the general consensus is that it likely has some effect. In one study, female infertility was significantly greater among women who had 5 or more drinks a week.
- Weight: Women who are substantially heavier or lighter than their ideal body weight are more likely to be anovulatory, and consequently infertile, than women who are within their normal body weight range. It has been shown that in obese patients, weight loss of even 10% can significantly improve pregnancy outcomes.
- Exercise and stress: Strenuous exercise and stress can lead to anovulation and infertility.
- Eating disorders: A history of eating disorders has been associated with anovulation and infertility. Excess weight may cause high levels of androgens (male hormones), which negatively affects ovarian function. Excessive thinness may cause a lack of estrogen, which can reduce fecundity.
PCOS—a hormonal disorder characterized by excessive androgen production—is the most common cause of anovulation. Although women who have PCOS can experience any of a variety of symptoms, the classic ones are anovulation, obesity, and hirsutism (excessive hair growth in unusual places).
Many PCOS patients are not able to properly process insulin, which contributes to their weight problems and also creates an increased risk for adult-onset diabetes.Metformin (Glucophage®) is a medication used to treat type 2 diabetes that also can reduce symptoms in women who have PCOS, although it is not approved by the U.S. Food and Drug Administration (FDA) for this use.
Recent studies show that metformin can help regulate ovulation, improve cholesterol levels, reduce abnormal hair growth, and decrease body mass index (BMI) in women with PCOS. Side effects include diarrhea, nausea, and vomiting. Herbs and acupunture have also been shown to help women with PCOS recover a normal menstrual cycle and to help regulate ovulation. Herbs should not be taken unless prescribed by a Board-certified herbalist.
The endocrine system regulates the production, actions, and interactions of hormones. Hormones are produced by the hypothalamus, pituitary gland, adrenal glands, thyroid gland, pancreas, ovaries, and testes. Diseases that affect any of these structures can lead to infertility, because the activities of all of the hormones are intricately interconnected. An excess or deficiency of any hormone can cause anovulation and infertility.
For example, in hypothyroidism, increased levels of prolactin (PRL) and thyroid-stimulating hormone (TSH) can affect levels of the sex hormones and may cause infertility. Hypothyroidism can be caused by failure of the thyroid gland, pituitary failure, or disorders of the hypothalamus. In hypopituitarism (failure of the pituitary gland), deficiencies of luteinizing hormone (LH) and follicle-stimulating hormone can produce amenorrhea (the absence of menstruation) and infertility in women, and impotence (erectile dysfunction) and infertility in men. Hypopituitarism can also cause TSH deficiency, which results in hypothyroidism.
Further, elevated prolactin levels suppress FSH and LH. In fact, high levels (hyperprolactinemia) can be considered "nature's contraceptive." Nipple secretion in non-lactating women (called galactorrhea) may be a sign of hyperprolactinemia. Causes include breast cancer, chest wall trauma, high stress levels, pituitary tumors, and enlarged pituitary gland.
Hyperprolactinemia usually can be treated medically. The gold standard for treatment is bromocriptine (Parlodel®). Pituitary tumors may require surgery.
Is there a link between environmental toxins and infertility? Although scientists and others speculate that infertility can result from exposure to any of a number of environmental toxins, the evidence is scarce and inconclusive, especially in women.
For example, researchers have shown that average sperm density (number of sperm per milliliter of semen) has declined dramatically over the past 60 years all over the world. It has been dropping steadily at 1 to 3 million sperm per milliliter per year, from more than 100 million sperm per milliliter in 1938 to less than 70 million sperm per milliliter in 1990. It is not exactly clear what has caused the decline, but it may be at least partially linked to exposure to various environmental toxins. Importantly, many scientists argue that it is not clear whether reduced sperm density causes infertility or not and that even though sperm density has been on the decline, it may not mean anything with regards to infertility.
The link between environmental exposure and infertility remains an important area of scientific research.