Menstruation is considered normal when uterine bleeding occurs every 21 to 35 days and is not excessive. The normal duration of menstrual bleeding is between two and seven days. Abnormal uterine bleeding occurs when either the frequency or quantity of uterine bleeding differs from that mentioned above or the woman has spotting or bleeding between her menstrual periods. Abnormal uterine bleeding may be caused by a variety of factors. The two most common causes are structural abnormalities of the reproductive system and ovulation disorders.
NORMAL OVARIAN FUNCTION
In women of reproductive age, the ovary secretes estrogen and progesterone into the bloodstream. These two hormones prepare the endometrium (the lining of the uterus) for implantation of a fertilized egg. The pituitary gland, located at the base of the brain, influences ovarian hormone production and ovulation by secreting two hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Following stimulation by FSH and LH, a follicle containing an immature egg begins to develop within the ovary. As the follicle enlarges, it secretes increasing amounts of estrogen. When a sufficient amount of estrogen is secreted, the pituitary gland releases a large amount of LH, which causes the follicle to release its egg (ovulation). If the egg does not become fertilized or does not implant in the endometrium, the secretion of estrogen and progesterone starts to decline approximately seven days after ovulation. With declining levels of estrogen and progesterone, the lining of the uterus is shed as the menstrual period (approximately 12-16 days after ovulation).
The cyclical release of FSH and LH from the pituitary gland is tightly regulated and easily disrupted. When the pituitary gland does not release appropriate quantities of FSH or LH, ovulation may not occur and the cycle may be disrupted. In some women who do not ovulate, the endometrium is stimulated by continuous exposure to estrogen without sufficient levels of progesterone to allow for complete shedding of the endometrial lining. This eventually may result in irregular or heavy bleeding. If estrogen exposure is continuous, cells within the endometrium also may become over stimulated and eventually develop into endometrial cancer.
CAUSES OF ABNORMAL UTERINE BLEEDING
Abnormal uterine bleeding (AUB) may be due to structural abnormalities of the uterus. Some of the more common structural causes of abnormal uterine bleeding include benign (non-cancerous) lesions of the uterus such as polyps, fibroids (myomas), and adenomyosis (uterine thickening caused by endometrial tissue moving into the outer walls of the uterus). Other causes include bleeding associated with early pregnancy, including miscarriage and ectopic pregnancy, as well as bleeding disorders that affect the ability of the blood to clot normally. Lesions of the cervix or vagina (benign and cancerous), chronic infections of the endometrial lining (endometritis), scar tissue (adhesions) in the endometrium, and the use of an intrauterine device (IUD) also may be associated with abnormal uterine bleeding. Additional causes of abnormal bleeding include medications that can affect the normal release of estrogen and progesterone; chronic medical problems such as diabetes mellitus or disorders of the liver, kidney, thyroid gland, or adrenal glands; or other medical problems that can affect the production and metabolism of estrogen and progesterone. Emotional or physical stress as well as significant changes in body weight may disrupt the pituitary’s release of FSH and LH and prevent ovulation.
ANOVULATORY OR DYSFUNCTIONAL UTERINE BLEEDING (DUB)
Dysfunctional uterine bleeding is the occurrence of uterine bleeding unrelated to structural abnormalities of the uterus or the endometrial lining. It is a diagnosis of exclusion made after structural causes of bleeding and chronic medical diseases have been ruled out. Other causes of abnormal bleeding must also be ruled out, including pregnancy complications and medications that influence hormonal action or affect clotting. Dysfunctional bleeding occurs more commonly in the first five years after a woman starts menstruating and as she approaches menopause, but it can occur at any time period. The cause of DUB is anovulation, the absence of ovulation and the orderly secretion of estrogen and progesterone, and may alert the woman and her physician to the fact that she is no longer ovulating normally.