In the second trimester, if the renal pelvis
dimension is more than 7 mm it is moderate hydronephrosis
and if it is more than 10 mm then it is severe. However, it needs to be assessed again in the last trimester where dimension of more than 15 is severe hydronephrosis. Therefore in your case you need not worry about the renal problems at all. For all purposes the readings are fine. Even with the FL and head circumference you need not worry. They can be re-assessed at a later stage. The discordance in your case which as you put it is "mild" is most commonly due to some difference in the date calculations of fetal gestation. So you can be at peace.