Placenta previa

Placenta previa is a severe, potentially fatal complication of pregnancy, in which the placenta attaches in the lower part of the uterus and covers all or part of the cervix, through which the baby must be delivered in vaginal childbirth. It greatly increases the risk for both premature labor and massive antepartum bleeding due to rupture of the placenta, which is abundantly supplied with blood vessels. It also can cause lesser bleeding in the second and third trimesters.

Detection of placenta previa during prenatal care usually leads to an elective caeserian section; detection during labor and delivery often leads to emergency surgery. Nevertheless, over 66% "of women with a distance of more than 10 mm from the placental edge to cervical os have vaginal delivery without an increased risk of hemorrhage."

Classification

The syndrome involves a range of placental positions:

• Total placenta previa occurs when the internal cervical os is completely covered by the placenta.
• "Partial placenta previa occurs when the internal os is partially covered by the placenta.
• "Marginal placenta previa occurs when the placenta is at the margin of the internal os.
• "Low-lying placenta previa occurs when the placenta is implanted in the lower uterine segment. In this variation, the edge of the placenta is near the internal os but does not reach it.