Previous cesarean delivery is a key risk factor for placenta previa because the uterine scar from surgery disrupts the endometrial lining, impairing normal implantation. This damage increases the likelihood that the placenta implants low in the uterus, covering or near the cervical os. The altered uterine environment from the scar tissue makes abnormal placental location more common in subsequent pregnancies. Other factors have less direct impact on placental attachment compared to the disruption caused by cesarean scars.

Reference: Williams Obstetrics, Cunningham et al., 25th Edition.