I would reiterate what Melissa said. I am also three months pregnant, and we used donor sperm (not from my CF husband). Both the donor and I tested negative as carriers, but they don't test for every genetic mutation. Anyone can still be surprised with a CF baby. It is far more common than people realize. At three months your wife should be able to get a test on the fetus rather than just testing the two of you. If it's really important to you to know ahead of time, I would suggest trying to do some prenatal testing on the fetus. Even if you and your wife are carriers, don't assume your baby will have it.
Congrats on the incoming baby! I want to tell you not to worry too much about things like this, but I am at the exact same spot and I am going crazy with worries about safe baby furniture, nutrition, and what it will be like to have a teenager in 15 years...
Good luck!