In a typical menstrual cycle, the uterus creates a lining called the endometrium. The biological purpose of the endometrium is to:
act as an area for a fertilized egg to implanthelp maintain a pregnancy if it occursshed as part of the menstrual cycle if pregnancy does not occurThe endometrium typically detaches and sheds gradually over several days. However, for some people, this shedding happens all at once. If this occurs, the endometrium may come out as one complete piece, called a decidual cast.
The medical name for a decidual cast is membranous dysmenorrhea. Exact data on the prevalence of decidual casts does not exist, but experts believe it is rare.
AppearanceThe name contains the word “cast” because the tissue that exits the body maintains the roughly triangular shape and size of the person’s uterus. For reference, a typical uterus measures 8 centimeters (cm) long, 5 cm wide, and 4 cm thick.
Decidual cast tissue generally feels fleshy, similar to a piece of skin. It can appear shiny and may be:
graypinkwhiteredblackcreamIn some instances, the cast may be very dark and resemble a large blood clot. Blood may also come out with it. The cast may feel solid or as though it contains fluid.