An example of the placental-myometrial interface in a third trimester fetus. This fetal evaluation was also for an intrathoracic finding on ultrasound. At no point was the placenta considered abnormal and the delivery was normal.
In this case, the interface may be harder to see because the thin myometrial layer is pressed up against the abdominal wall, but it is still normal. Often it is useful to try to trace the outer myometrial wall and work inwards, to at least feel comfortable that placenta percreta and increta can be excluded.
The placenta normally develops a more heterogeneous signal intensity when >24 weeks.