I had one ICSI cycle - had 5 eggs collected from 1 ovary (couldn't get to the other one). Only 2 fertilised - had 2 day transfer of both (both Grade A) because it was 9 years ago and I was 39 - SET in its infancy- both stuck, b/g twins the result.
Cycle 1 - 1 grade 1 embie put back at day 2 - BFP but mc Cycle 2 - 2 grade 3 embies put back at day 2 - chem preg Cycle 3 - 1 grade 1 embie put back at day 3 - chem preg Cycle 4 - 1 grade 2 embie put back at day 3 - BFP (fx, still going)
At my clinic grade 1 is best but my "best" embies didn't succeed!
I had two "poor grade" embryos transferred, I was 38 and they were the only two still developing by day 3. They didn't tell me the exact grading they used at the time. My clinic (Guys) is very focussed on SET but even so they recommended we put both back. I was happy with that and came out of ET feeling pretty despondent as to our chances. They both stuck and we had twins, now aged 4
Prior to that I'd had a private cycle, and put back two grade A embryos which were supposed to be "almost perfect". Neither stuck....
At the time I remember reading around the subject and finding that the whole grading system is quite controversial and there's some evidence to suggest that it has next to no correlation with outcome. It's far from an exact science.