During the reproductive years, two of the hormones made by the ovaries - estrogen and progesterone - play important roles in the menstrual cycle. In preparation for a fertilized egg, estrogen causes the endometrium (lining of the uterus) to start to thicken. Progesterone then causes a ripening or secretion of nutrients. If a fertilized egg is not received in the uterus, the ovaries stop making these hormones, and the uterine lining is shed as the menstrual period. Each woman has a pattern to her periods, which differs from woman to woman.
A few women simply stop menstruating one day and never have another period. Most women, however, go though a longer perimenopause and experience changes or irregularities in their menstrual periods. These irregularities are caused by secretion of erratic levels of ovarian hormones and decreased frequency of egg release (ovulation). Initially, the menstrual changes can be subtle. Usually a woman's cycle will get shorter, with periods occurring more often than every 28 days. Bleeding may last fewer or more days than previously, and blood flow may be heavier, lighter, or just spotting. Late in perimenopause, skipping periods becomes common. However, some women skip several cycles and then menstruate regularly again. Any menstrual pattern is possible - but each woman will know that, for her, a change has occurred.

Hormonal imbalance. Irregular or heavy bleeding can be caused by the poor ovulation that occurs as the ovaries begin to decline.

Hormonal contraceptives. Use of products such as prescription contraceptive pills, implants, injections, and intrauterine devices can cause spotting or breakthrough bleeding, particularly in younger women. Spotting refers to a small amount of bleeding from the vagina that occurs at the monthly time for a period. Breakthrough bleeding occurs at a time other than the monthly time for a period. Until menopause is reached, pregnancy can occur and cause abnormal uterine bleeding as well as missed periods. For most women, these changes are natural and normal during perimenopause, and no treatments are needed.

These noncancerous growths in or around the uterus are a very common cause of abnormal uterine bleeding. While some fibroid tumors produce no symptoms, others can produce dramatic changes in periods (such as prolonged and/or heavy bleeding), menstrual cramps, back pain, and difficulty with bowel movements or urination. While the cause of fibroids is unknown, their growth can be stimulated by estrogen surges that sometimes occur during perimenopause. Fibroids may shrink after menopause when the ovaries reduce production of estrogen. Occasionally, estrogen replacement therapy stimulates their growth once more.
Other uterine lining (endometrium) abnormalities. Noncancerous growths, such as polyps, in the endometrium can result in abnormal uterine bleeding. In a very small percentage of cases, some types of cancer in the uterus, vagina, and cervix can cause abnormal bleeding from the uterus and/or vagina. Regular pelvic exams and Pap smears are particularly helpful in diagnosing these serious diseases early enough for effective treatment. Factors that interfere with blood clotting sometimes cause uterine bleeding. In addition, although bleeding passing from the vagina usually comes from the uterus, it is possible for the vagina or cervix to be the source of bleeding.

There are several procedures a clinician can use to determine the cause of abnormal uterine bleeding, including the following:

This is a widely used procedure often performed in a clinician's office, and no anesthesia is needed. A small sample of the uterine lining is removed through the cervix (opening to the uterus from the vagina) then examined by a pathologist. Endometrial biopsy is often used to exclude cancer, and it can sometimes identify other reasons for bleeding.

In this surgical procedure, the cervix is dilated and the uterine lining removed by scraping or by suction and scraping. Because it usually requires anesthesia, D&C has decreased in frequency due to endometrial biopsies.

In this procedure, a tiny telescope is inserted into the vagina and through the cervix to view the uterine lining directly. A biopsy can usually be done at the same time if there are any observed abnormalities.

This painless procedure uses sound-generated images, similar to the ultrasound images used during pregnancy. The images are obtained with a probe inserted into the vagina. Although it is less invasive than surgery, transvaginal ultrasound can sometimes miss small abnormalities.

In this variation of ultrasound, saline is infused into the uterus to enhance visualization of the uterine cavity.

When abnormal uterine bleeding is caused by internal changes in levels of estrogen and progesterone, it can often be regulated with prescription hormones, such as low-dose oral contraceptives. Other prescription hormonal drugs, such as progestogens, are also sometimes used for short-term treatment.
If nonsurgical treatments fail, several surgical procedures are available, depending on the cause of the abnormal bleeding. If fibroids have been diagnosed, the decision to surgically remove them depends on their size, number, and location, as well as the severity of symptoms and a woman's desire for more children. Many of these procedures are used to remove fibroids, but they can also be used to evaluate and treat other kinds of abnormal uterine bleeding.

A tiny telescope (laparoscope) is inserted through a small incision in the abdomen. Pelvic organs can be viewed through the laparoscope and, sometimes, fibroids or ovarian cysts can be removed.

A laser or electrical loop is inserted into the uterus through the cervix. Growths or polyps that bulge into the uterine cavity can be removed.

The uterine lining is destroyed by freezing, heating, or cauterization. It cannot be used when fibroids are the problem, unless the fibroids are also removed.

Valuable in the past for determining the cause of abnormal uterine bleeding, but as a treatment, it seldom cures the condition of severe, consistent abnormal bleeding. Today, other surgical treatments are generally considered better options.

Uses an abdominal incision to remove uterine fibroids (typically performed under general anesthesia).

Uses small plastic beads inserted into the uterine artery to block the blood flow to the fibroids, causing them to shrink. Indicated for women with fibroids who can't  or don’t want to undergo surgery. Usually performed on an outpatient basis.

About 30% of all hysterectomies in the United States are performed for fibroids, and others are done for abnormal uterine bleeding. The uterus (and sometimes the cervix) is removed along with any fibroids that may be present. Afterward, pregnancy is no longer possible. The ovaries may or may not be removed (Oophorectomy). If both ovaries are removed (bilateral Oophorectomy), immediate surgical menopause occurs.

Periods stop when a woman is past menopause, but taking some hormone treatments can cause bleeding to resume. Unless the bleeding is the typical pattern caused by taking hormones, women who have uterine bleeding after menopause (12 months with no menses at all) should see a clinician immediately to rule out serious causes, such as cancer.

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