I can just about prove that cutting early caused a twisted umbilical for me last season. And I know for a fact it cost me my first pied baby, that one had a twisted umbilical as well.
I guess my thoughts on this are, read up on it, because the knowledge can help save a baby if the worst happens. But as to cutting early? When I do cut now, it's only after one pips, and only the tiniest of openings. I don't do that whole top of the egg off thing I see so much of.
Gale