This prospective cohort study was conducted in Arash Women’s Hospital between August 2014 and August 2015 to define the relationship between caesarean section scar and placental implantation and migration. Seven hundred and thirty women with one previous birth (caesarean section or vaginal delivery) and a singleton pregnancy underwent three ultrasound examinations for placental evaluation at 11–14, 20 and 34 weeks gestation. Previous caesarean section was related to the increased odds of anterior placental implantation but no relation was seen between low‐lying placenta or placenta praevia and previous caesarean. The placental migration from low‐lying to non‐low‐lying position was similar between women with and without previous caesarean.