Thanks @ECM1981. I requested the single freezing because I'm only looking at doing single transfers. CFC's preference was to put 2 in the straw in case one didn't survive the thaw...but then what if both thawed perfectly. I couldn't discard a perfectly healthy embryo. Apparently they don't refreeze well. So I'd end up transferring 2 when the aim for me is single transfers. I had to do a bit of standing up for myself to get the embryologist to agree to single freezing, and they wanted to charge me extra to do it. However after they charged me an extra $2k for SD1's sperm I think they waived the extra 'small' fee for single freezing.