Period Clots Usually Form If You Have A Really Heavy Flow.
First, a mini-primer on blood clots in general.
When you think about clots of blood, you might imagine the kind that come together when you have a cut. Your body springs into action, combining enough platelets (blood cells that adhere to each other) and proteins from plasma (the liquid part of your blood) to plug the injured blood vessel, the Mayo Clinic says. This is how clots help to stop bleeding.
Blood can also clot in your veins, especially if you have risk factors like being pregnant, which causes hormone changes that increase your blood clot risk, or recent surgery, because moving less also contributes to this hazard. These clots can dissipate without harm, but sometimes they can be life-threatening.
The blood clots that can emerge from your vagina during your period are a bit different than these other types, though. Period clots are comprised of the endometrial lining that builds up in your uterus in preparation for pregnancy, then sloughs off during your period when you don’t conceive.
Clots are normal, but they typically happen when a [person] has a heavy flow.
This is in part because a gushing period prompts your body to form clots so you don’t lose more blood than you should (around two to three tablespoons over the course of your entire period). Also, the opening of your cervix (the narrow passage at the lower end of your uterus) is pretty small. If you have a substantial flow, that allows the blood to build up in your uterus, Dr. Ruiz explains, giving components like platelets and plasma proteins time to congeal.