What is the earliest embryonic stage that placenta accreta could occur?

Answer 1

Placenta accreta is a condition in which the placenta invades into the myometrium (muscle layer of the uterus) instead of remaining in the endometrial layer (interior lining) as it should. Theoretically, the earliest stage of embryonic development when this could occur is at the blastocyst stage (which is actually pre-embryonic). This is the stage when a zygote/conceptus typically implants into the endometrium and the placenta begins developing from the trophoblast cells, so placenta accreta could not occur before this stage. Practically speaking, it may take enough time to invade deeply enough to reach the myometrium that the conceptus may be in the gastrulation phase or beyond when the myometrium become involved.