THE MANY CAUSES OF INFERTILITY

Given how important hormones are to egg maturation and ovulation, it’s not surprising that hormonal imbalances are a common cause of female infertility. Low levels of luteinizing hormone and follicle-stimulating hormone, for example, may prevent ovulation or make it erratic. Even slight irregularities in the hormone system can prevent the ovaries from releasing eggs. Specific causes of such hormonal imbalances include injury, tumors, excessive exercise, and starvation. Some medications are associated with ovulation disorders, and some studies have shown that stress can negatively affect fertility, as can poor nutrition.

Some women suffer from polycystic ovary syndrome, a condition defined by the presence of multiple ovarian cysts that impair ovulation, and associated with the production of excessive amounts of androgens (the “male” sex hormones, typically present in lower amounts in females). This syndrome is one of the most common hormonal disorders, affecting an estimated 10% of women of reproductive age. In addition to impairing ovulation, the condition is associated with irregular menstrual cycles, diabetes, and obesity.

One of the most common causes of infertility in women, especially those living in Western industrialized societies, is advanced maternal age (typically defined as over 35). Women often have a harder and harder time becoming pregnant as they age, and after age 35 they may choose to consult a fertility specialist to assist in becoming pregnant. Age-related declines in fertility occur in part because both the quantity and quality of a woman’s eggs decline with age. At birth, a woman has about 1 million follicles in her ovaries. By puberty, she has about 300,000 follicles. Of these, only about 300 will ever ovulate an egg. Fertility in women peaks around age 25 and declines thereafter. As a result, according to the Centers for Disease Control, by age 40, nearly half of all women will experience difficulty in conceiving.

Men, too, experience declines in fertility as they age, as testosterone levels fall, but usually not as quickly or as dramatically as women. Men produce sperm throughout their lives and therefore can still father children in their 50s, 60s, and 70s. However, many men suffer from other problems, such as erectile dysfunction and testicular varicose veins, that can interfere with sperm reaching their target.

About a third of all cases of infertility are caused by reproductive impairments in women, and about a third are caused by impairments in men. In the remaining cases, the impairments affect both men and women or the cause of infertility cannot be determined (INFOGRAPHIC 30.8).