Menstrual clots are likely normal; Giddy interviews Dr. Santoro on when to see a doctor
“Menstrual clots are a sign that a woman is bleeding heavily,” said Dr. Nanette Santoro, 
the E. Stewart Taylor Chair of the Divisions of Reproductive Endocrinology and Infertility & Reproductive Sciences, department of obstetrics and gynecology. “Menstrual blood is designed not to clot,” she continued. “The uterus bleeds, but along with the blood comes agents that break down blood clots. So, as the blood is getting ready to be expelled, it’s pretreated with fibrinolysis that breaks down the clot. When women are bleeding too quickly for the menstrual blood to get treated by the clot-dissolving molecules, the blood clots.”
Menstrual clots are common and typically there is no cause for concern. However, there are situations where seeing a doctor is important.
“Women who pass many [clots] are likely to be bleeding more than average and may be at risk of anemia, or they may have a structural problem with the uterus that is causing heavy menstrual bleeding,” Dr. Santoro said. “Menstrual bleeding that is causing a woman to change a pad or tampon every two hours for more than a day is enough to alert her that she should be checked out.”