vman on "How many blasts did you have from your day 3 embryos?"

I am in the middle of the wait to hear how many blastocysts we will end up with.

How did it go with your donor egg cycles? Once you had a certain number of good quality day 3 embryos, how many of those became good quality blastocysts?

I have heard 50% mentioned a lot, but 50% of what? Fertilized eggs? Day 3 embryos of any quality? Good quality day 3 embryos?

Thanks for any answers!