High Risk Pregnancy
Placenta previa occurs when an embryo implants itself in the lower uterus and the developing placenta thereby implants low in the uterus and covers the internal cervical os. The previa can be complete, which involves the placenta covering the internal cervical os completely, or partial, which involves only a portion of the placenta covering the cervical os. The diagnosis is of placenta previa is often made in the second trimester by ultrasonography testing and is monitored for placental migration away from the os which occurs with uterine growth. Placenta previa in the second trimester puts the client at risk for developing vasa previa and thought to be a result of inflammatory atrophic changes to the placenta. In the third trimester, placenta previa is the leading cause of painless bleeding leading to hemorrhage. The bleeding occurs as the placental attachment is disrupted from thinning of the area as the cervix and uterus prepare for labor. Due to the location of the placenta, the uterus is unable to contract to stop the flow of blood from the vessels. When bleeding occurs, Thrombin is released and stimulates uterine contractions, which thereby disrupt the placental attachment from the uterus even more, causing increased bleeding and can eventually lead to hemorrhage (Joy, 2012). The incidence of placenta previa is in approximately one in 200 pregnancies, has a mortality rate of 0.03%. Common risk factors include previous placenta previa, previous cesarean births, suction curettage for miscarriage, carrying more than one baby, delivery of six or more pregnancies, and tobacco or substance abuse (Perry, Hockenberry, Lowdermilk, & Wilson, 2010). For first time pregnancies, placenta previa occurs in about 1 in 1,500 pregnancies but the risk for women who have had more than five pregnancies increases to about 5 in 100 pregnancies.
J oy, S. M. (2012, June 5). Placenta Previa. Retrieved September 29, 2012, from...