Thread: placenta previa

why is bleeding in placenta previa painless?

Pathophysiology
Placental implantation is initiated by the embryo (embryonic plate) adhering in the lower (caudad) uterus. With placental attachment and growth, the developing placenta may cover the cervical os. However, it is thought that a defective decidual vascularization occurs over the cervix, possibly secondary to inflammatory or atrophic changes. As such, sections of the placenta having undergone atrophic changes could persist as a vasa previa.


A leading cause of third trimester hemorrhage, placenta previa presents classically as painless bleeding. Bleeding is thought to occur in association with the development of the lower uterine segment in the third trimester. Placental attachment is disrupted as this area gradually thins in preparation for the onset of labor. When this occurs, bleeding occurs at the implantation site as the uterus is unable to contract adequately and stop the flow of blood from the open vessels. Thrombin release from the bleeding sites promotes uterine contractions and a vicious cycle of bleeding-contractions-placental separation-bleeding.

I hope from this pathophysiology you'll get your answer, while this isn't the case in abruptio placenta which is painful. Read pathophysiology of both.