What is the cause of placenta accreta?

Don't know: We don't know all the causes, but we know certain folks are at increased risk, such as having multiple c-sections and placenta previa.

Uterine scars/defect: The placenta tends to implant over pre-existing uterine scars or defects; when that occurs, the invasive nature of the placenta can lead to abnormally increased vascularity in areas without sufficient uterine muscle to control the bleeding once the placenta is delivered (particularly near the cervix). That is potentially life-threatening if undiagnosed until delivery and managed in small hospital!