Renal pelvis dilatation. Or moderate?

Dear Doctor, My baby was diagnosed with renal pelvis dilatation during 20weeks of my pregnancy, it was 4mm in left kidney and in follow-up on 36weeks scan it was 6mm and after his birth (male baby), on the 4th day of scan it was 8mm and neonatologist advised that it may go away as the baby grows in most cases and advised to have repeat scan after 45days. We have done scan on 52nd day and found the dilatation has increased to 11mm and we are literally worried and stressed about it. However our pediatric advised that in few cases it may increase slightly and then gradually decrease so we have to wait and watch and advised to have next scan after 90days. Is it really possible to get the dilatation increased and then decrease? Please advise on the possibility and is 11mm during 52days is mild or moderate? Kindly advise the next step to be taken. Regards, Monica