Originally, the title of Nyoin was bestowed only to empresses, especially to those who had become a kokumo (mother of an Emperor); after Princess Shoshi, the daughter of Emperor Gorezei's chugu (second consort), was made Nyoin (Nijoin) in 1074, however, some women received the title simply because of their noble bloodlines, rather than because they had given birth to a child of the emperor.
初期の女院号宣下は后妃の中でも特に国母となった者に限られて行われたが、承保元年（1074年）の後冷泉天皇中宮章子内親王の院号宣下（二条院）以後、所生はなくても尊貴な出自を以って院号を得る例が加わった。