yep - that was me... always had perfect looking embryos but after going through 4 stims & 10 transfers (with unexplained infertility) we did a pgd cycle. got 7 embryos to biopsy and only 2 were 'normal'. not saying that you need to do pgd, but it provided me with more information i guess. btw - we had all the blood tests too (karyotype, blood clotting etc) and they all came back normal too. we were told that our pgd results were what they would expect to see from a batch of embryos (ie they cant all be viable). also we were told that down syndrome embryos can look like the best quality. again, not saying this is the case for you, just agreeing with n2l that you really cant tell the viability just by looking at them/counting cell numbers. pop over to the pgd thread if you have questions, the ladies in there are more than happy to answer any questions (including me!).