"Hearst Magazines and Yahoo may earn commission or revenue on some items through these links." For most uterus owners, periods are a monthly occurrence as regular—and annoying!—as rent.

A decidual cast is a large, intact piece of the uterus' lining expelled from the body during menstruation. The collection of tissue, blood, and mucus retains the same shape as the uterus.

For most uterus owners, periods are a monthly occurrence as regular—and annoying!—as rent. And between bleeding, PMS symptoms, and the cost of period products, it's not always a great time.

Leaños-Miranda A and Cárdenas-Mondragón G (2006) Serum free prolactin concentrations in patients with systemic lupus erythematosus are associated with lupus activity. Rheumatology 45: 97–101 ...