A friend of mine had IVF and two embryos put back and ended up with only one egg implanting but had identical twin girls
I watched a fascinating programme a while back about multiples and discovered you can have identical triplets

not sure about quads etc. also identical twins can be one boy and one girl if the sperm has a certain abnormality that make it carry both male and female chromosomes

and it said on there that twins sharing a placenta must be identical (for obvious reasons) but twins with their own placentas may be identical or may be fraternal and they can't tell for sure until they're born . So even if a scan shows boy/girl twins you still can't rule out them being identical until birth, then there are twins that are called mirror image twins , one will be left handed and one right handed and they look identical but as if one was looking in a mirror and the other was the image so everythings reversed ,I found this particularly fascinating as they said this could account for left handed people as they haven't discovered a gene for being left handed and it doesn't seem to be passed down to offspring so they thought every left hander may be the sole survivor of a mirror image twin pregnancy

made me a bit sad really as i'm a left hander and so is one of my DD's, and I did have early bleeding with her but didn't get a scan until 12 weeks ,and my mum had a lot of bleeding early in her pregnancy with me
The octuplet woman in america had six eggs put back and all implanted and she ended up with two sets of identical twins as well

I think stuff like thats the reason why two is the max here, although 3 still seems pretty common in america . Very fascinating subject though maybe because it's relatively rare for us humans