Hi I also have the above. But as I am having c-section, my gynae said I don't really have to worry as it's usually harmless. Just cannot walk too much, do strenous exercise, carry heavy stuff, squat, etc. But if you plan to have natural delivery then will be a problem as not possible if its blocking the 'exit', so your sister may have to consider c-section if the placenta doesn't move up. http://www.babycentre.co.uk/a830/low-lying-placenta-after-20-weeks-placenta-praevia