What is infertility?
Infertility is the inability to get pregnant (conceive). It is typically diagnosed after a couple has tried to get pregnant for 12 months without success. Infertility may also be diagnosed when a woman has been able to get pregnant but has been unable to carry a fetus to term (miscarried).
Infertility affects about 10-15% of couples in the United States. About one-third of cases are due to women's problems with fertility, another third are due to men's problems, and the remaining are due to a combination of men's and women's infertility issues.
Fertility depends on the successful timing and interaction of many factors. Hormones produced by glands, including the hypothalamus, pituitary, and thyroid glands, as well as by a woman's ovaries and a man's testicles 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 is 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, leaving about 200,000 to 400,000 follicles. Throughout a woman's reproductive years, the few hundred thousand available eggs will be further reduced in number with a total of about 400 mature eggs 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, estradiol 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. The combined effects of these hormones 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. Some of the causes of infertility are easy to identify and fix, while others are more complex.