Possible causes of placenta previa include a scarred endometrium (lining of the uterus), a large placenta, an abnormal uterus, or abnormal formation of the placenta. The incidence of placenta previa is approximately 1 out of 200 births.

The incidence increases with each pregnancy, and it is estimated that the incidence in women who have had 6 or more previous deliveries may be as high as 1 in 20 births. The incidence is doubled in multiple pregnancy (such as twins and triplets). Risk factors include multiparity (previous deliveries), multiple pregnancy, previous myomectomy (removal of uterine fibroids through an incision in the uterus), and a previous C-section (if the scar is low and close to the vaginal cervix region).