Low placenta?

At my anatomy scan the tech told me my placenta was low. They want it at above two centimeters and I'm at 7mm. Does anyone know what this means or what complications come with it? She said it might move up when my uterus grows...but that's not for sure and I don't know if it's something i should be concerned about. It's at least not placenta previa but that's all I know. She also told me my placenta is posterior...if that helps at all lol