What is infertility?
In females, infertility is the inability to become pregnant (conceive) or the failure to sustain a pregnancy that results in a live birth (miscarriage). In males, it is the inability to impregnate a partner. Infertility is typically diagnosed after a couple has had 12 months of unprotected, well-timed intercourse without a resulting pregnancy. It may also be diagnosed when a woman has been unable to maintain a pregnancy.
Fertility depends on the successful timing and interaction of many factors. Hormones produced by the hypothalamus, pituitary, and thyroid glands as well as by the ovaries and testes play an important role in controlling and supporting reproduction.
In order for a successful pregnancy to occur, a woman must develop and release an egg from one of her ovaries. Women are born with a fixed number of eggs (oocytes), each of which are contained in a fluid-filled cavity in the ovaries called a follicle. At birth, there are 1-2 million follicles; however, by the time of puberty, most have degenerated (atresia), leaving between 200,000 to 400,000 follicles. Throughout a woman's reproductive years, the several hundred thousand available eggs will be further reduced in number with only about 400 mature eggs in total released, about one per month.
After a woman's menstrual cycle begins, follicle-stimulating hormone (FSH) causes several follicles to mature; however, usually only one will dominate. During this time, estrodiol production increases, peaking at day 14 of a typical 28-day cycle, causing the uterine lining to thicken and stimulate the production of the hormones gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), and FSH. These hormones in concert result in the release of an egg from a mature follicle, initiating the process of ovulation.
Once released, the egg travels through the fallopian tube and is fertilized by a man's sperm, forming an embryo, which moves into the uterus and implants within the thickened uterine lining (endometrium). As the embryo grows, the placenta forms, nourishing and supporting the fetus throughout the gestation period. Problems with infertility can be associated with any one or more of these processes.
An estimated 10% of American women (6.1 million) are infertile. Some of the causes of infertility are easy to identify and resolve, while others are more complex, involving one or both partners. About 58% of infertility cases are due to female problems and 25% are related to male concerns. Approximately 17% of cases show no clear identifiable reasons for infertility.