Your dentist won't be happy. Crunching ice = toothbreaker.

I did have diagnosed UTI (very low level) and also thrush at the beginning of my first pg. The thrush of course got a lot worse as soon as I took antibiotics. I just decided to run with the cranberry in a state of desperation when the 2nd one started coming on very shortly afterwards, the pharmacist couldn't give me a strong contraindication at the time so I decided it was the lesser of two evils. I used it as a preventative, and if the symptoms had worsened I would've gone straight to the Dr - UTIs can get bad in pregnancy (because your immune system is suppressed) and turn into kidney infections so that's not something you want to ignore.

It's always worth discussing with your OB or GP, or even pharmacist, before you start to self-medicate.