Placenta previa is an obstetric complication that occurs in the second and third trimesters of pregnancy. It may cause serious morbidity and mortality to both the fetus and the mother. It is one of the leading causes of vaginal bleeding in the second and third trimesters.
Placenta previa is generally defined as the implantation of the placenta over or near the internal os of the cervix.
- 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.
Pathophysiology
The exact etiology of placenta previa is unknown. The condition may be multifactorial and is postulated to be related to multiparity, multiple gestations, advanced maternal age, previous cesarean delivery, previous abortion, and possibly, smoking.
Unlike first trimester bleeding, second and third trimester bleeding is usually secondary to abnormal placental implantation. next
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