I'm curious too. I've never heard of it being a problem - in fact, I've heard it as a blessing - when the baby is implanted high, since placenta previa isn't a concern.
I do think implantation sites can move, although I don't understand why. Often when a low lying placenta is diagnosed, the doc will say well don't worry too much, it may move up, and often it does.
If it's too high in the corner of the uterus,where the fallopian tube joins in, there might not be enough room for the baby to grow, and it would act like a tubal pregnancy, ie an ectopic. But hopefully it's in a spot where there will be enough room. You'll probably feel unusual discomfort if something is wrong, so if you're feeling well, I'd be optimistic.
I just googled it, and apparently it's an issue. I can't find any explanation for why it's an issue, though.
Brandie, can you call your doctor and get clarification?
The implantation site can't move, but I'm curious as to why your doctor and thinks it's a problem. I know low lying placentas are dangerous, but I've never heard anyone mention high implantation before.