Screening for placenta previa usually involves the use of an ultrasound, or a test that uses sound waves to create an image of the fetus. This ultrasound can reveal the placenta’s location, and show doctors how much of the placenta is covering the cervix, which helps in diagnosing the condition. A vaginal ultrasound may allow for a more accurate evaluation.
Please note that in early pregnancy, an ultrasound may show a low-lying placenta. However, only in a small percentage of cases will this condition develop into placenta previa. In most cases, the placenta will move upward and away from the cervix as the uterus expands; this is referred to as placental migration.