@mrkb I found this paper really helpful at laying out the risks. It's from 2020 and it had data from hundreds of thousands of births in England, so the stats seem quite robust:
www.bmj.com/content/371/bmj.m3377/
What shocked me was that 43% of first time mums had a "complicated" delivery even in the low-risk category. They defined "complicated" as severe tears, instrumental delivery, EMCS, low apgar score and a couple of other things. In the supplementary info they have a breakdown of what that 43% was and it's mostly tearing, EMCS and instrumental delivery.
It's a very clearly written paper and they are very up front about all the different categories and outcomes (although you have to look at the supplementary info for the really fine detail).
For me, those figures are really high. I think a lot of stats are presented across all births, not just first time births, which masks the high risk in the first delivery.
For severe tears I think the big risk factors (from other papers not this one) are a large baby, back to back or breech labour, the baby being overdue, instrumental delivery and (maybe) an epidural.
It's not as simple as just refusing all interventions though, because you end up swapping one risk factor (epidural) for another (later, larger baby). And then possibly adding the epidural back on top of labor doesn't begin spontaneously.
Although I'm technically in the low-risk category, my baby is tracking quite big (90th centile), he's currently back to back and I'm not far off 35. To me, all those things make me really hesitant to play the numbers game. If I could guarantee a non-complex birth I would be happy but the odds aren't much better than tossing a coin!