I actually just spoke with my doctors about this very subject today. I will start taking Kalydeco aka VX770 and would like kids down the road so we talked about what that means. Basically since there are no studies the risks outweigh the benefits of taking the drug.
Once pregnant you would stop taking Kalydeco. Unless of course, the benefits of the drug truly outweigh the unknown risks, then that would be quite the conversation between patient and doctor.
However, my doctor informe me that once on the new drug that TTC will become easier since it will thin out cervical mucus considerably.