Objective: The primary objective is to determine whether the concentration of cell-free fetal DNA circulating in the maternal plasma is significantly increased in women with morbidly adherent placenta (MAP) compared to women with placenta praevia and previous caesarean. Secondary objectives are to determine whether cell-free fetal DNA circulating in the maternal plasma is a useful biological tool to detect MAP, alone or in addition to the imagery findings (ultrasonography and RMI), in a high risk population (placenta praevia and previous caesarean or only prenatal suspicion of MAP).