5 day vs 3 day embryo transfers

Actually, I think the success rates are very close, so it shouldn't make much of a difference.

Yes, pregnancy rates have not been determined to be better with either transfer...

However, a Day 5 embryo has a better chance of implantation simply because it's been "selected out" than a Day 3 transfer, giving one the chance of transferring fewer embryos for an equivalent pregnancy rate

So why is it that we always don't wait till the Day 5?

sometimes the embryos arent doing all that great out of the womb so they put them in hoping they will do better in there.

So the transfer all depends on how the mebryos are doing.