Lou my doctor usually transfers on day 3, but he did say that he was having a lot of success with day 2 transfers for a while...but then he changed back to day 3 and i think its because the culture they grow the embryo's in has gotten better, so he likes to leave them in the culture a little longer so that the time between transfer and implantation is shorter.
I spoke in depth with the scientist last time and she said that with blasties, the ones that dont make it that far wouldn't have become blasties in the womb, even if they were transferred on day 3. So i asked her why dont they grow all embryo's to blasties then, so that the ones that make it to blasties are the only ones they transfer?
She said that it depends on the egg numbers that they get. If they get alot of eggs and try and grow them all to blasties, you may end up with quite a few blasties and they dont freeze or defrost as well as day 3 embryos. So they try to transfer on day 3 so that you get a transfer and you get embryo's to freeze for future FET's.
With day 5 transfers, the embryos are checked everyday and if they dont look like they are advancing to blastie then your doctor may call you in to have the transfer because of the theory that they may do better inside than out and that it is better for the patient to have a transfer than not to psychologically.
So i think they try to transfer embryo's in any case, just so the patients feel like they are getting somewhere and to give the embryos the benefit of a doubt, hence why they usually transfer on day 3 before they become blasties, so that they dont even know the outcome.
One could argue that they are better off inside your womb at the day 3 stage, but they aren't meant to be, they are meant to be in the fallopian fluid in the tube. The culture that they are in until transfer is supposed to replicate that fallopian tube fluid and feed and nuture the embryo until it is just about ready to implant.
Once it is transferred i imagine that the closer it is to the stage that it can start to feed and nurture from your lining until the placenta is formed, the better (so blastie). But if they do that all the time you:
1. In the case of lots of eggs you may get lots of blasties that don't freeze so well ... or
2. In the case of only a few eggs...get nothing to transfer
The conclusion i come to is that if they get lots of eggs they should see how they are doing on day 3 and freeze the best looking ones, grow the remainder to blastie and transfer on day 5 if they make it. If they dont make it then they wouldnt have anyway. At least you have many frozen day 3 embryo's and they can defrost a few at a time and only transfer the ones that make it to blastie.
If they only get a few eggs then they should try and grow them to blastie and only transfer the ones that make it, because the ones that dont, wouldnt have anyway, so you dont have to endure the TWW. In this case you would have alot of ladies that end up with nothing to transfer, but to me its better than going through 2 or 3 transfers with no result IYKWIM.
I figure that this is the answer that they dont have. Whether it is better to have nothing to transfer (so no false hope) or repeated transfers with repeated TWW with embryo's that they have no idea whether that they will implant or not. I guess that would have be a personal choice.
So if they transfer it on day 2 or 3 or 5 is a hard one to answer, i don't think they even know. Hence why they change it all the time.
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Megan36  Kim35
After 3.5 long years of IUI and IVF/ICSI
Noah Lee was born by Emergency C-Section at 27w4d @ 750gms
Due to Antepartum Hemorrhage and Placental Insufficiency
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Day2/3 TF 
waiting to hold our baby in my arms 
In my heart always 
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