Michinaga set the precedent for Ittei-Nigo (an emperor having two empresses) when he made Teishi, who was the second consort of the emperor at the time, empress, and made his daughter, FUJIWARA no Shoshi, the new second consort.
道長は先に中宮であった定子を皇后とし、娘の藤原彰子（しょうし）を中宮に立てて、一帝二后の先例を開いた。