Varies. Placenta previa is a condition in which the placenta implants directly over the cervix and blocks the birth canal. For this reason, women with placenta previa require a c-section. Since the placenta is exposed more, it is more prone to bleeding as well. Bleeding ranges from continuous or occasional spotting to torrential hemorrhage that could threaten the lives of both mother and baby.
Unknown. 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.
See below. It's variable and unpredictable.