Well from what i have read on the net you can get ferning around the time AF is due if you are pregnant but some wome get ferning at other times in their cycle because of high estrogen i have used the MB a few months and only ever get ferns a few days leading up to O but to be honest deep down i don't think i am pregnant so i will wait a few more days as i only O'd 10 days ago.
Please don't get your hopes up girls i don't want to let you all down.