What symptoms come with decidual bleeding? how common is it in people under 20 years of age?

A pregnancy issue: Decidual bleeding is the name for vaginal bleeding/spotting during pregnancy that may occur around the time that a pregnant woman would otherwise expect her menstrual period. The phenomenon is fairly rare and usually does not last longer than the first few months of pregnancy. It is thought to be related to shedding some of the uterine lining outside of the placental area with hormone fluctuation.