I hope I have the same success as Trans-Siberian! We also chose to transfer 1 great quality, 8-cell, highest grade on day 3. I have been agonizing ever since the transfer (beta on Tuesday the 16th) and wondering if I should have done two… but for what it’s worth, the chances with my one are a little over 40% and with two would only be about 10-15% higher, with a 20-25% chance of twins. For a somewhat small margin of higher success but (what I consider) a much higher chance of twins, we opted for one and not two transferred. It is such a tough choice. I’d be lying if I said I don’t go back and forth every hour about this. But, what’s done is done, and if this one doesn’t stick we’ll transfer two in a FET (we have 4 leftover).
Everything I have researched has said that an excellent quality embryo has only a slightly lower chance than two embryos. As others have said, it comes down to the risk of no pregnancy vs. twins, and what you can live with.