Placenta over cervix. Placenta previa is a complication of pregnancy where the placenta is covering the opening of the uterus called the cervix. It occurs in 1/200 pregnancies more commonly in patients with a previous c section. If diagnosed in early pregnancy it may resolve before delivery. If not a C-section will be needed. It can cause painless bleeding often requiring bedrest.
Placenta over cervix. The placenta, the interface between mother and fetus, is normally located in the upper uterus. If it is in the lower uterus and covering or partially the cervix, bleeding is likely to occur when labor starts. Delivery must be by scheduled c-section. Sometimes such placenta can be abnormally attached to the uterus as well as abnormally located, and this can cause additional complications.
Abnormal implanting. Previa: Placenta overlies the cervix/birth canal. Gr 1 means placenta is close, Gr 4 means it's directly overlying/blocking the baby's exit -- high chance of preterm labor & bleeding; you'd need a C/S at 36-37wks. More common in woman w/ hx of C/S & smoking. Not much you can do but wait. If dx'ed early, the uterus still grows/stretches and a placenta can migrate away even in 3rd tri. Follow w/ US.