Hi Alex...i can't see how bringing on AF would effect your FET. I know when i had to take Primolut to bring on AF, I asked if it would effect my cycles or anything, and they just said that the primolut mimicks the last 7 days of your cycle with hormones etc, and once you stop it after 7 days, AF will arrive and it will just shed your lining like in a normal cycle, so i don't think it will effect your FET (but someone please speak up if i am wrong!!!)