Ultrasound. Ultrasound is the main way to follow a previa. If your previa resolves with time, your labor should be the same as anyone else's. If it doesn't, tests for anemia, clotting factors, and blood availabilty are tests that are performed to be prepared for any emergency at delivery. Most patients are at bed rest in their 2nd trimester and pelvic rest until delivery.
Ultrasound. 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.