The pre delivery scans report shows the fullness of the kidney
. That means stagnation of urine in the pelvis part of the kidney. This is also called as hydronephrosis
. This is either due to blockade outflow or reflux backward. This is commonly found in the routine antenatal scan. Usually it disappears sometime after birth.
Moreover the degree of fullness is to be taken into account - mild, moderate, severe. Even if severe nothing to worry, It can be tackled easily and prognosis is good.
As your Dr suggested, wait for some more days, it will regress (commonly regresses)