I am not sure Jennie or I have have completely explained or described what placenta accreta is and why it is so rare and dangerous. I attempted to make some basic drawings to better describe the condition in relation to the mother (in this case the uterus) and the fetus (mainly the placenta).
The drawing below demonstrates the proper relation between the placenta and the layer of the uterus that it is normally supposed to bond with to create the placental barrier. The endometrium is easily regenerated and the amount of nutrients etc. are regulated by hormones. This is the layer that is sloughed off (usually monthly) during the cyclical pattern of hormones.
Normal placenta and endometrium
The following graphic is a representation of a placenta accreta situation. The thin endometrial base layer nearest the muscle layer gives rise to the regenerating endometrium to replace the sloughed off layer, and after implantation, thickens the endometrium to better provide for the placenta. Since the endometrium is designed to remove itself from the base layer after birth, blood loss is ususally minimal. When the placenta covers an area that had previous scar tissue such as resulting from a Cesarean section, DNC, or something else, this base layer of cells is no longer there, there is no layer specially created for the reception of the embryo or the placenta. During development in placenta accreta, the fetal placenta will bind with the scar tissue in stead of the nutrient rich endometrium. Severe hemorrhaging will most likely occur once the placenta pulls away from the scar tissue.
Placenta accreta example
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