It became the first example of junbo that in 1087, in the succession of Emperor Horikawa to the throne, his elder sister, Imperial Princess Teishi was equated with his mother because his real mother, Chugu (Empress) FUJIWARA no Kenshi was already deceased, after that, junbo was named in the case that an infant emperor succeeded to the throne after his real mother passed away, or the case that although his real mother was alive, her social status was too low or she was already a nyoin (a woman bestowed with the title "in" [title given to retired emperor]).
准母は堀河天皇が践祚に際して、既に生母である中宮藤原賢子が崩御していたため、寛治元年(1087年)に皇姉てい子内親王が母に擬せられたのが初例となり、爾来、天皇の生母が死去した後に幼年で即位した場合や、生母が存命だが身分が低すぎるか既に女院となっている場合などに、准母を定めるようになった。