Hmm the dreaded decision of 1 or 2 embryos... It's a tricky one, with no "right" answer really.
We had IVF 4 years ago, and as we were 35 at the time, decided to go for 2 embryos to be transferred.
A few weeks later, we had 2 beans on board - identical twins according to the sonographer. Turns out they were ID, and were born by c-section at 35.2 weeks. They spent 4 days in SCBU, just to receive a bit of help, nothing serious.
As far as the twin pregnancy went, it was very straightforward. No complications, very minor morning sickness was all. Waters went at 35.2, otherwise I think they would have held on to full term.
It was hard at first, I won't lie. The twins were not good sleepers, and suffered badly from reflux. We decided to use savings and take on a nanny for a few months to give us a break. We used a night-nanny occasionally too, to give us both a decent nights sleep.
Now, they are two boistrous 3 year olds, who play together (and fight together) a lot
. They are completely different personalities, with one being right-handed, and the other left. So, looks like there's some mirroring going on there.
We've just had DS3, who was a singleton. That pregnancy was much, much harder on my wife than the twin one. No major complications as such, but crippling morning sickness, and tiredness.
For what it's worth, in your situation, I'd advise putting 2 embryos back. Bear in mind though, that the odds of identical twins increases by virtue of undergoing IVF. In our case, if the second embryo had stuck, we'd be looking at triplets!