Unequal Placenta Sharing

Today the doctor told me that one of my twin boys is smaller than the other..Baby B is in the 50 percentile and baby A is in the 33 percentile. They say it's from unequal placenta sharing being that they share a placenta. It can't really be treated I just have to be monitored closely to make sure A gains some more weight. Has anyone pregnant with mo di twins been diagnosed with unequal placenta sharing??