This was the reason why there were many crisis of discontinuity of Imperial succession after the Medieval Period, even though the system of the Inner Palace in premodern time was well established.) there were even examples of an Emperor allowing his child to be adopted into the hereditary Imperial Family to secure the succession of descendants, if there was a crisis of the discontinuity of the family.
前近代の後宮制度の充実ぶりにも関わらず、中世以後に皇統断絶の危機が何度も生じたのはこうした事情がある）状態にあったが、世襲親王家が断絶した場合には天皇が実子を養子として送り込む事で子孫の安泰を図る事も行われた。