Menstrual blood clots are a natural part of the bodys defense mechanism and are a mixture of blood cells, tissue, and blood that are expelled from the uterus during menstruation. They are more common during the first two days of menstruation, which is typically the heaviest part of a period, and generally occur when the flow is heavy. 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. Menstrual clots can be bright in color, or a darker, deeper red, and more sizeable clots may look black.

Passing blood clots during a menstrual cycle is often a normal occurrence during the heaviest days of the period. However, heavy bleeding and passing large clots can sometimes be a cause for concern. 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 menstrual pad every two hours or less, for several hours.

Although it is normal to have clots in the blood during menstruation, this symptom can sometimes signal a medical issue. Some potential causes for large blood clots during a period include thyroid conditions, polyps and fibroids, birth control, and medications. Menstrual bleeding is considered heavy if a person changes their tampon or menstrual pad every two hours or less, for several hours. If someone is passing clots and thinks they could be pregnant, they should seek immediate medical help as it could be a sign of miscarriage.

In summary, menstrual blood clots are a natural part of the menstrual cycle and are generally nothing to worry about. However, if someone is passing large clots or experiencing heavy bleeding, they should seek medical advice.