@Fakedelight: Oops can't PM you until you have 5 posts!
I don't know if you have consecutive miscarriage/chemical pregnancy or not. If you did and with good grade 5 days embies, I would recommend to do NK cell testing. I only know 3 FS that aren't too conservative about doing the BT and biopsy here in Perth. I think GP can even order the BT. As for implantation failure, again, if you have good grade embies, I would recommend implantation screening BT. I've a list of all these. Happy to provide in PM. I can also send you the FS names.
Check out Dr. Sher's blog on IVF or implantation failure. He is a known FS in the States.
Oh...one thing I don't quite understand. What OHSS has to do with blastocyst? Blastocysts can be developed from whatever number of eggs you are having. Although I suspect OHSS patients can get less quality embies and thus don't get to blast stage?