Just as described, Mizuko was a notion that included not only dead fetuses, but also children who have died during their infancy or in early childhood; however, due to the explosive increase of abortion in Japan after the war, the meaning which is used in the present day began to take hold as the custom of mizuko kuyo (a mass for a body lost through miscarriage or abortion) spread from around 1970s.
水子とはこのように、もともとは死亡した胎児だけでなく乳児期、幼児期に死亡した子供を含む概念であったが、戦後の日本で人工妊娠中絶が爆発的に増加したことを受け、1970年代ごろから中絶で死んだ胎児の霊を弔う水子供養の習慣が広まっていくとともに、現在の意味が定着していった。