This is called a decidual cast. It occurs when the lining of a woman's uterus sheds as one massive solid piece of tissue during her period. : r/MakeMeSuffer

Fleshy Mass Passed Vaginally by a Young Woman

During menstruation, why doesn't the entire uterine lining shed at

Decidual Cast: Structure, Symptoms, Causes

What Is A Decidual Cast During Menstruation?

Decidual Cast: What Is It, Symptoms, and When to Seek Help

Everything You Need to Know About a Decidual Cast

Decidual cast: What it is, causes, risks, and more

Decidual Cast: What It Looks Like, Causes, Risks

Decidual cast: Definition, symptoms, causes, and more

I think I passed a decidual cast (TMI PICTURE)

What is a decidual cast? See photos and learn the cause behind it