Lil Chookie, some stats that may help... For single embryo transfers in a woman under 35, a day 3 embryo has a success rate of around 20%. If you go to blast, the success rate increases to 42%. However, there is always the risk that they won't make it. My FS is one of those dead set against transferring two, but he's a big fan of blastocyst culture and has quite emphatically stated to me on a number of occasions that if an embryo can't get to blast it was never going to work anyway. He also says the same thing about embryos surviving thaw - if they don't defrost, they were never going to work... Doesn't make it much easier when you're the one getting to transfer and finding that there's nothing to transfer in the end... Happened on my last FET.

As the others have said, it's an intensely personal decision. For me, even if my FS would allow it, we'd never transfer two as my health conditions make the thought of twins incredibly daunting.

Try to trust your FS, they are the ones with the experience and the knowledge.

BW