In the U.S., about 10% of women ages 15 - 44, or about 6.1 million women, have problems getting pregnant or carrying a baby to term.

Age

Fertility declines as a woman ages. Fertility begins to decline when a woman reaches her mid-30s, and rapidly declines after her late 30s. As a woman ages, her ovaries produce fewer eggs. In addition, the quality of the eggs is poorer than those of younger women. Older women have a higher risk for eggs with chromosomal abnormalities, which increase the risk for miscarriage and birth defects. Older women are also more likely to have health problems that may interfere with fertility.

Weight

Although most of a woman's estrogen is manufactured in her ovaries, 30% is produced in fat cells by a process that transforms circulating adrenal male hormones into estrogen. Because a normal hormonal balance is essential for the process of conception, extreme weight levels (either high or low) can contribute to infertility.

Being Overweight. Being overweight or obese (fat levels that are 10 - 15% above normal) can contribute to infertility in various ways. Obesity is also associated with polycystic ovarian syndrome (PCOS), an endocrinologic disorder that can cause infertility.

Being Underweight. Body fat levels 10 - 15% below normal can completely shut down the reproductive process. Women at risk include:

• Women with eating disorders, such as anorexia or bulimia.
• Women on very low-calorie or restrictive diets are at risk, especially if their periods are irregular.
• Strict vegetarians might have difficulties if they lack important nutrients, such as vitamin B12, zinc, iron, and folic acid.
• Marathon runners, dancers, and others who exercise very intensely.

Smoking

Cigarette smoking can harm a women's ovaries and contribute to a decrease in eggs. Studies show that women who smoke are more likely to reach menopause earlier than women who do not smoke.

Alcohol and Caffeine Use

Alcohol and caffeine use may contribute to infertility.

Environmental Factors

Exposure to environmental hazards (herbicides, pesticides, industrial solvents) may affect fertility. Estrogen-like hormone-disrupting chemicals are of particular concern for infertility in men and for effects on offspring of women. Phthalates, chemicals used to soften plastics, are under particular scrutiny for their ability to disrupt hormones.

Stress and Fertility

Neurotransmitters (chemical messengers) act in the hypothalamus gland, which controls both reproductive and stress hormones. Severely elevated levels of stress hormone can, in fact, shut down menstruation. Whether stress has any significant effect on fertility or fertility treatments is unclear.