What does it mean for baby to have fluid in kindey?

I’m pregnant with my first i’m 37 weeks and 2 days, i went to the doctor Wednesday and they did a ultrasound and then after that i waited to see the doctor and she came in the room and told me that my baby has more fluids in his right kidney and she told me not to worry that when he’s born they’ll check him to see whats going on. So my question is has anyone else gone through this before and if you have how do you deal with it? im really worry.