Montesmum - Sorry to hear about your results, that must be so frustrating. I hope the last one is a sticky star!
Chances - not sure if there is a magical number. In my IVF cycle I had 10-12 follicles, 7 eggs collected, 6 fertilized all developed well, 1 blasto transferred (DD) and the other 5 frozen, FS and embryologist thought it was a great cycle. I don't think the numbers will predict the quality you will get. And apparently only 50% of perfect looking embies are sticky. Its amazing that BFPs actually happen - but they do.