28 week ultrasound with twins

So went for my ultrasound today the twins have gained a little more weight but went from the 7&8th percentile last month down to the 3rd percentile this month meaning they have stopped growing In Length so now waiting for the call from Albany to go there and see what the next steps are the dr said as long as they are moving (which they are non stop) then not to stress to much. 
Any other twin mommies to be every have this problem ?