Hi Saffy, so sorry you have to worry about this on top of the stress of the TWW. I did some research on this myself as before doing assisted hatching I had never had an expanded or hatching blast. This info is both good and bad, good in that blasts expand and compact, bad in that expansion is a good sign after being frozen.

There’s another interesting feature of blastocysts and that is their ability to expand- and contract. Expanded blastocysts may “collapse” in culture and look unexpanded. With time, the blastocyst will re-pump the fluid and “re-expand”.* A “compacted” blastocyst is likely a transient condition in which the fully pumped up blastocyst has “deflated’. As long as the blastocyst is capable of expansion, this temporary deflation is not a problem. In fact, prior to vitrification, many programs routinely deflate their blastocysts to optimize the vitrification procedure. After freezing and thawing, a sign of recovery is re-inflation or re-expansion of the blastocyst, showing that the embryo is alive and pumping- literally.". Not sure of this helps, I hope some.

But in saying that some one just told me after my recent transfer that all FSs and labs want good stats, if they did not think your embie had a good chance they would not transfer and would have thawed your other one. Don't give up hope before it is over. Wishing you all the best. Xx