[MeredithD]

Just thought I would add something to this interesting debate. Personally, I do feel that not every embie that doesn't make it to day 5 wouldn't have made it in the body and have certainly heard plenty of stories of "poor" looking day2/3 embies ( that would be thought not to have made it to day 5) which went on to preduce healthy babies.
However, I read very recently ( sorry can't remember where) that there is NO correlation at all between what an embie looks like at day 3 and its potential to get to blast. From first hand experience, I have just finished a round of IVF/PGD ( sadly not successful). I got a summary of the embryology report and the grade of day 3 embies didn't really predict at all what they looked like a few days later. One of my B grade day 3 embies turned out to be the best by day 4 and was actually transferred
My point in all this, is that maybe the thinking that "poor" day 2/3 embies would never have become children if were left to go to day 5, is not necessarily true. They could well have fought on and become great blasts which still would have been transferred to bring a healthy pg. Similarly, transferring the "best" day 3 embie isn't going to guarantee the one that truly can go the distance. I guess I am still leaning in favour of the blast transfer.