I actually took estrogen during my LP - not FP - so think follow others advice on this one. Using estrogen during your FP will suppress your natural FSH. This can cause your follicle to develop slowly. For me, I have used 0.02mg ethynyl estradiol during days 1-6 while stimming and it slowed the follicle growth. Once I went off of it, the follicles seem to respond better.