Blood clots during menstruation are a natural part of the bodys defense mechanism. Menstrual clots are a mixture of blood cells, tissue, and the thick, jelly-like texture of a menstrual clot helps prevent too much blood from escaping. Menstrual clots generally occur when the flow is heavy, and they are more common during the first 2 days of menstruation, which is typically the heaviest part of a period. Clots can be bright in color, or a darker, deeper red, and more sizeable clots may look black. The consistency of menstrual blood varies both throughout the period and from one period to another, and people may experience a heavy flow containing menstrual clots one month, and a lighter flow with no clots the next month.

While blood clots during a period are normal and rarely a cause for concern, passing large clots may be a sign that something is wrong. Heavy bleeding and passing large clots can sometimes be a cause for concern. Some potential causes for large blood clots during a period include thyroid conditions, polyps and fibroids, birth control, medications, and miscarriage.

It is advisable to seek medical advice if the clots are larger than a quarter in size, are very frequent, or occur with an abnormally heavy flow that requires a person to change their tampon or pad after less than 2 hours. Women who have menorrhagia usually bleed for more than 7 days and lose twice as much blood, and if you have bleeding that lasts longer than 7 days per period, or is so heavy that you have to change your pad or tampon nearly every hour, you need to talk with your doctor.

In summary, blood clots during menstruation are normal and rarely a cause for concern. However, passing large clots may be a sign that something is wrong, and it is advisable to seek medical advice if the clots are larger than a quarter in size, are very frequent, or occur with an abnormally heavy flow that requires a person to change their tampon or pad after less than 2 hours.