I believe canesten pessaries are safe while pregnant.

If you are really worried and would like a more natural remedy, you can use probiotic capsules. They simply add more of the friendly bacteria found naturally in the vagina which restores the balance and bye bye thrush. I had a resistant strain of thrush once, all the canesten in the world did nothing, but the probiotic "pessaries" turned out to be the only thing that worked in the end.

BW