We do lots of back to back cycles, meaning period then birth control pills and have no problems with quality of eggs. I prefer to put donors on birth control pills as it's very easy for them to get pregnant after donating, even after telling them you don't ovulate on time, you are more fertile etc. One month we had six donors get pregnant the month after donating - that would be a nightmare wouldnt it? So, I like bcp cycles and starting stims on day 2 of withdrawal bleed from bcp. Egg numbers ARE compromised if a donor is on bcps for over 21 days, so 21 days on 7 days off 21 days on is better than staying on pills, The body needs the lh surge in the 7 days off pills.