Emmy, surely a hospital would be protected if the woman signed something saying she didn't want a cannula during labour? It would only be problematic for the hospital if they'd forgotten?

Anyway, surely they'd be able to get one in when they realised you needed it - my last birth I had a cannula put in and they had a fair bit of trouble with it, but I'd had a fast birth at home and had lost quite a bit of blood by the time I got to hospital - nothing anyone could have done about that really, just one of those things that happened. But I imagine, after birth, if they realised 'ooh, we might just pop a cannula in', surely they'd have a bit of time up their sleeve before it got difficult?
I imagine it's just a convenience thing (which I guess I understand), but if the situation called for it I imagine someone good at cannula's could be called in? That happened a few times with me, once when they couldn't find a good vein, and another time when it tissued.

Anyway, that was rather a ramble, but I'm just thinking, surely if you're AT a hospital, it's not going to be that hard to put a cannula in after the birth if it's needed?

Or is the issue if you ask for drugs of some sort? Do you need an IV line for that?