In addition, the system of making an imperial princess an honorary empress (a woman who was not the consort of the emperor but nonetheless held the title of empress) to serve as a foster mother to the emperor began with Imperial Princess Teishi (Ikuhomon-in), daughter of Emperor Shirakawa; this system was later extended to allow "院" (a kanji pronounced "in" that means "imperial court") to be added to the end of the title of an honorary empress by imperial decree, and the system was further extended by Princess Akiko (Hachijo-in) in 1161 to allow "院" to be added to the title of any female member of the imperial family.
また、皇女を准母立后による尊称皇后（天皇の配偶ではない称号のみの后）とする制度が白河天皇皇女媞子内親王（郁芳門院）を契機として確立すると、院号宣下の対象も尊称皇后にまで拡大、さらに応保元年（1161年）のあき子内親王（八条院）によって、后位を経ずに院号宣下される道も開かれた。