Dr said fluid in the baby kidneys

Hi friends, I did my 18 weeks ultrasound yesterday and dr said that there was fluid in my little princess kidneys. I already read a lot of things about it in 18 weeks. It is saying that is because the kidneys already are working so probably he saw at the time that was full of amniotic fluid. Please tell me something you know. He said on the screen of 32 weeks gonna check again😕😰😨