Sonogram of placenta previa and placenta previa accreta

(A) Placenta previa. Sagittal transabdominal scan shows the placenta (P) centered over the cervix (C). There is a normal hypoechoic area between the placenta and the bladder. 
(B) Placenta previa accreta in a different patient from (A). Oblique sagittal transvaginal scan shows the placenta (P) centered over the cervix (C). Note how the placenta invades the myometrium, with loss of the hypoechoic layer of myometrium (arrow), which can be seen in the above panel where the previa is not complicated by accreta.