kidneys can affect fluid levels. bub is constantly swallowing fluid and then weeing it out (so it goes through the kidneys). generally though kidney problems cause too little fluid. some times too much fluid is caused by swallowing problems.

Thats just my limited knowledge, and very generalised. so please dont freak out or anything, just saying ONE possible cause!!! Did your Ob say anything that might be causing it? or are they just keeping an eye on it?

*hugs* hope everything is ok.