After I had had so many failures I decided to do the same as you, to transfer 2 blasts and 1 that was not very good, infact it was a day behind. I'm absolutely sure that one of my twins is the day behind one as it always measured a day behind on the scans. I'm in favor of single embryo transfers, especially at blastocyst and I honestly believe that putting in 2 blasts will increase the odds of twins. Are you ready for twins? If not, I hope you don't mind me saying but I'd do a single transfer. Good luck minniet, this has just got to be your success story.