<prompt> Low-lying placenta is when the edge of placenta is ___2cm away from the internal os2.5 cm away from the internal os2 cm away from the internal os2.5 cm away from the internal os  <response>: When the placental edge is 2cm from, but not over, the internal os, the placenta is defined as low-lying placenta. The diagnosis of low-lying placenta is made by the ultra sound examination. Ref: Williams Obstetrics 25th edition Pgno: 774 