Birth control before ivf

I’ve been doing research on ivf. Ive seen some posts where people seem to go on birth control for the month before ivf. Why is this?

Has anyone not used birth control and just gone straight to ivf?

My cycle is completely normal. I’ve gone through all the testing and meet with the doctor next week about my results and next steps. I just want to be prepared with questions. Plus for insurance purposes, I’m trying to do ivf or iui before the end of the year! (Our deductible is met this year!!)