My transfer was cancelled so on day 3, my doc froze the embryos. I had 11 total, and 7 he thought would make to blast. (I think that means 7 looked really good and would survive to day 5?)

Why didnt he just wait it out till day 5 to freeze them? He told me his reason is when it's time for my transfer, he will thaw four of the best ones and watch them grow 2 more days. Why didnt he just do it now?

I dont understand the reasoning behind that and I know absolutely nothing about freezing embies. We couldnt really discuss it further because we didnt have time. Any insight?