The last cycle when I fell pregnant I used MB (which I had been using for months) as well as an OPK for the very first time. I got a + with OPK on the Monday and then I didn't get the real ferns with MB until about Thursday. We BD'ed from the previous Friday through to a week after MB said I O'ed, so we caught whichever one was right. I'm due earlier than I should be for my LMP so I think the OPK was more accurate than the MB.

I also found I got ferns towards the end of my cycle. My GP said its because its picking up the increase in progesterone that you have after ovulation.

Good luck everybody!