I'd never had my B12 levels checked. To this day I have no idea if I was deficient or not.
However, that wasn't the basis for me doing the B12 shots. Below is info I shared with someone about this. As for how much per shot, I'd have to check but I'm sure it was at least 1 ml and maybe as much as 2 ml.
I did the B12 shots because I had read about how it is important fuel for cell energy and that it promotes healthy cell division. Since I had very poor division with my embryos in the petri dish, I reasoned that I could compensate for that once they were transferred back. And then once we decided to move on to DE I still felt that I would benefit from it since that too obviously involves a transfer of an embie.
Using B12 shots to promote better cell division for embies is NOT anything I found documented. I want to be clear about that - don't want to mislead you that I found evidence to support its use for embie cell division. BUT, I did read plenty that indicated that adequate levels of the B vitamins is important for fertility as well as read that there is no medical harm or risk to take a B12 shot(s). And I didn't need to read that part, because DH has always taken B12 shots from his doctor and later a nurse friend who would administer for him. He suffers from bad allergies that drain and fatigue him so the B12 shots in his case, are for energy. But once I became a whiz with injections, I started giving him the shots...and then eventually this last cycle I started taking them as well.