My clinic prefers to do IVFs with single-blast transfers. I was a bit stunned to hear it because my anecdotal information from the discussion forums I frequent told me that women in their 40s often have up to 3 embryos or blastocysts put back in. Sometimes more than that, but that is not considered so cool these days.
For a long time the medical community has been recommending the higher quantity on the premise that, well, 40-somethings are more likely to get a sticky pregnancy that way. We are. But we are also more likely to get pregnant with multiples. Simple math, really.
(I do not subscribe to the romance of wishing for twins. My uterus has been compromised enough that the risks of trying to carry multiples seem clear to me. Then there are the obvious risks to the babies. Would I say no to twins? Why would I? But I have to agree that it is safer and more reasonable to actively try to get just 1 at a time.)
Now studies are showing that we may have just as decent a chance with a single transfer. It's all about the quality, of course. But if you transfer 1 good-quality blast, pregnancy chances are looking just as good as if you transfer 2 or 3.
My first RE said that he would recommend 3. That matched the info I'd seen so far and so I didn't press for his reasoning at that time. He may very well have been assuming that my egg/embryo/blast quality would be bad and so didn't even discuss the other option with me. So I don't know his opinion on the 1-blast tx for his patients overall. He was definitely a worst-case scenario guy. And I did appreciate that in many ways.
When my current RE first mentioned (because I asked) that she'd want to transfer 1 of whatever we got, my position was, "Oh, how can this be? We can't possibly drain our savings on the assumption that this has no chance. This is all-or-nothing. How could we bank on just 1 measly blob of our cells? At least with 3 perhaps 1 might be of sufficient quality to make it OR we'd come out of this experience with enough info to tell us, conclusively, that nothing will stick, not even 3 top-shelf cell blobs nurtured and manipulated by the best reproductive scientists we can afford."
The RE assured me that the final recommendation would be made based on the actual quality of whatever we're working with. It's just that their preference is — and success rates are backing it up — to transfer 1 nice-looking blast at 5 days. If the embryos at 3 days aren't looking hip to surviving in the dish much longer, then whatever is viable will go back in then. Success can and does and doesn't happen under both scenarios.
My feeling is that I have to trust my clinic to do what they do best. That's what their success rates are based upon and where they came up with a prediction for our odds. And we just can't know what we're dealing with ahead of time.
For your reading pleasure:
"IVF Technique Enables Pregnancy Without Multiple Births, Stanford Researchers Find"
"2-for-1 Is No Baby Bargain, Doctors Say"