DD1 had this, i'm pretty sure it got picked up at the 20 week scan,and was told that 1 kidney was a bit smaller than the other.Had quite a few u/s following after that.At 30 weeks she had slowed right down with growing and had c-section at 35 weeks.She was born 5p 5oz
I am surprised that yr doc doesn't know about it and hopefully someone at the hospital follows it up for you