Fluid in Kidneys

I had my 20 week ultrasound early this week and baby boy is healthy, but apparently has fluid in his kidneys. The ultrasound tech and my midwife both said it's fairly common in boys and usually clears up before the baby is born, but they're referring me to a bigger hospital 45 mins away for a level 2 ultrasound. Part of me is worried, part isn't.... has anyone been through a similar situation?