Shazey
b*gger they wouldnt give you time off for scan

from my limited understanding :-k

most clinics (but not all) prefer to go to blasts if you get over 6 eggs - they tend to sort out the best and strongest embryos - that you can't see at day 2-3 -but going to blast means may not end up with snow bubs (frosties)

When blasts go back they are in uterus at day 5-6 it is day they would be naturally - where as normally day 2-3 embies are still normally travelling down the fallopian tubes instead of in uterus.

having said that lots of people get pregnant from 2-3 day old embryos and not from blasts - but I've seen lately more going to blasts.

Hope your follies continue to grow and DR has good news for you