Abnormal Blood Clots During Menstruation

A monthly period is just part of life for women of child-bearing age. The amount and type of menstrual blood can vary from one woman to another and, in some cases, the flow can include blood clots. This can be normal, especially when it only occurs on and off for a few days. But in some cases, the presence of especially large clots or heavy flow with many clots could indicate a problem in the uterus.

Uterine Fibroids

Heavy menstrual flow including blood clots larger than roughly the size of a quarter may signal a problem, such as a noncancerous uterine growth called a leiomyoma, or fibroid. Roughly 70 percent of white women and 80 percent of black women in the U.S. develop one or more fibroids during their lifetime, according to the authors of a January 2003 "American Journal of Obstetrics and Gynecology" article 18. Although many women with fibroids experience no symptoms, about 25 percent report heavy menstrual flow that may be accompanied by blood clots, note the authors of an October 2013 "American Journal of Obstetrics and Gynecology" research report 1. Although the exact cause of fibroid tumors is not known, they tend to run in families.

Uterine Changes

Any condition that causes increased menstrual flow can also lead to blood clots. This is especially relevant if the blood pools in the uterus or its flow out of the uterus is obstructed, giving the blood extra time to clot. For example, a woman who has had multiple pregnancies or given birth to twins often has a slightly enlarged uterus, which might allow uterine blood to pool and clot before flowing into the vagina. A condition called endometriosis, in which the uterine lining overgrows, thickens and becomes abnormal, can also lead to pooling of uterine blood and clots in the menstrual flow.

Other Causes

Another type of growth in the uterus, called a polyp, might also slow flow of blood out of the uterus. Usually a noncancerous growth, a polyp develops in the uterine lining and can protrude into the uterine cavity. A protruding polyp can interrupt outflow of blood from the uterus, allowing it to clot. While polyps may not cause problems in many women, they might interfere with implantation and have a negative impact on fertility, according to a review article published in the September 2012 issue of "Human Fertility." In rare cases, the presence of uterine cancer could lead to abnormal bleeding that might also include blood clots 7.

When to See Your Doctor

When menstrual blood clots are accompanied by heavy flow and pain, this can interfere with quality of life for many women. Although there may not be any immediate risk to a woman experiencing this problem, the American College of Obstetricians and Gynecologists recommends that a woman experiencing clots and heavy bleeding see her doctor.

Women experiencing heavy flow and other symptoms that might indicate a serious problem should seek medical care right away. These symptoms might include: -- dizziness or fainting, especially on standing -- rapid heart or breathing rate -- paleness, weakness and lack of energy -- fever or chills -- unexplained weight loss