I had a rollercoaster ride of ultrasounds with my 2nd son where they told me all the same things as you and more. At his 1st ultrasound at 15 weeks his bladder and kidneys were enlarged. So we had a ultrasound every month after that. They said I could have to abort (NO WAY!!!), have surgery before he was born (YIKES!!), have problems all his life etc... It was the scariest time and each month we would get on the rollercoaster of emothions again. I have family history of kidney problems BUT they still said it could be chromosome abnormality etc... Near the end of my pregnancy they finally convienced me (against my better judgement) to induce him so it wouldn't "get worse". My son was born and the hospital staff couldn't even tell, not even the peditritian that checked his kidneys. Of course I made them do an ultrasound and then they could see that his kidneys were still enlarged but he was fine other wise. We did have to do a surgery at 3 months and at 11 months but he has never had any infections etc... with his kidneys.
I was glad to know that they needed some attention BUT I should have stopped getting ultrasounds after the first one and just let GOD take care of me and him.
The stress that the ultrasound techs and staff put on us was HUGE and my husband will not go through that EVERY AGAIN. I didn't do an ambio since it does have great risk involved and it wouldn't have changed anything, even though they PRESSURED us to do it. I was having my baby no matter what! He is now 3 and no one can tell he ever had anything wrong.
Since I had some family history (my sister and myself had kidney problems as kids) you would think that they would just say that was it and go on but they didn't. So see if you have any family history of badder issues, if so, that is it, if not... don't worry (easier to say then do) and don't let them pressure you in to ANYTHING you don't want to do.
GOD bless.