I think that women with CF that are wanting to get pregnant have to look at what their personal situation is. How high are their PFTS, what is their weight, stress level, do they have regular menstral cycles, how often do they have lung infections. If the woman has thick cervical mucus that can work against the process as well. These are all factors that work with or against a person becoming pregnant. On average I believe it takes a healthy person around a year to concieve. If you are a pretty heathy CF patient it may take more or less time. There is no definite time frame. You should always discuss with your doctor how they feel your health is right now and if you need to make changes to make a pregnancy possible. If a person cannot sustain their own body, then they are not going to be able to sustain a pregnancy.
Much Love
And Good Health