A woman of child-bearing age has a monthly period that usually lasts about seven days. The amount and type of menstrual blood can vary from woman to woman and, in some cases, the flow can include blood clots. This can be normal, especially when it only continues on and off for a few days, but in some cases the presence of especially large clots or a heavy flow with many clots could indicate a problem in the uterus.
Fibroids and Menstrual Clots
When a woman's menstrual flow is especially heavy and contains blood clots larger than the size of a quarter, this may signal a problem, such as the presence of 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 research paper published in January 2003 in the “American Journal of Obstetrics & Gynecology.” Although many women with fibroids experience no symptoms, about 25 percent of women with these uterine growths report heavy menstrual flow that may be accompanied by blood clots, note the authors of an October 2013 research report published in the “American Journal of Obstetrics & Gynecology.” Although the exact cause of fibroid tumors is not known, they tend to run in families.
Uterine Changes and Clots
Any condition that causes increased menstrual flow can also produce blood clots, especially 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, if a woman has had multiple pregnancies or given birth to twins, her uterus might be especially large, allowing 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 cause pooling of uterine blood, allowing clots to appear in the menstrual flow.
Another type of growth in the uterus, called a polyp, might also slow flow of blood out of the uterus. Usually a non-cancerous growth, a polyp develops in the uterine lining, called the endometrium, 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 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.
Seeing 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, who can recommend a course of action.