All are true regarding Duncan's placental separation except :

Marginal seperation (Mathews-Duncan) : seperation stas at the margin as it is mostly unsuppoed. With progressive uterine contraction more and more areas of the placenta get seperated. It is found more frequently. central seperation (schultze) : seperation stas from the centre resulting in opening of few uterine sinuses and accumulation of blood behind the placenta.With increasing contraction more detachment occurs facilitated by the weight of placentaand retroplacental blood until whole of placenta is seperated. Reference: Dutta Textbook of Obstetrics 7th edition page no 122