I think SG is very particular about what they freeze. When I left after my day 5 transfer, I had three remaining blastocysts. The RE said two look very good and had a good chance of making it to freeze and the third he was doubtful about. The two that looked good looked so good that he did not want to risk transferring a second one. I was shocked when I rec'd the call four days later saying none of them made it to freeze.