What is placenta previa?
Placenta previa is a condition where a low-lying pla-centa covers the internal cervical os; it occurs in about 1/200 deliveries. Predisposing factors include multiparity, advanced maternal age, and prior cesarean section.
The previa may be marginal, partial, or complete. With a complete placenta previa, the placenta covers the entire cervical os, thereby preventing vaginal delivery of the fetus. Incomplete coverage of the cervical os is referred to as a par-tial placenta previa. A marginal previa is a partial placenta previa associated with a low-lying placenta and minimal placental coverage of the cervix. In a low-lying placenta, the placenta is implanted in the lower uterine segment but does not cover the internal cervical os.