Hmm, I wish I had the articles here to give a link but I will have a look later and post them. In my own words-
There has been research done looking at a correlation between oestrogen levels and their effect on the sodium chloride channel...basically when you are ovulating you lose even more of the ion transport function that people with CF are already lacking. This possibly means that if you pick up an infection during this time the environment of the lung surface will be more ripe for infection...which SUCKS!!! I have noticed my chest feels heavier the first couple of days of my period, especially if it's a heavy one. And then I just feel SO much better when it's over...but doesn't everyone?!