if you do a fully medicated cycle (estrogen until a simulated "o" date when lining thick enough, the combined estrogen and progesterone until BT) you shouldn't get a visit from AF - AF arrives when your progesterone levels drop. if you're doing a HRT FET you'll find that, when you get your BFP, you have to stay on the meds til around 10-12 weeks.

i had two medicated FET's and didn't get AF either time until several days after stopping the meds.

some people only have partially medicated cycles - estrogen supplements to help develop lining, and then they O naturally and produce their own progesterone from corpus luteum - in this case, AF will arrive whenever the progesterone falls if the cycle is unsuccessful