My cousin tore so badly with her son that she started researching birthing positions while TTC #2. She suggested birthing on all fours for a larger baby and had no issues birthing her 9 pound daughter with no stiches.
perineal massage might help (I read somewhere using evening primrose oil was useful). During pregnancy and labour even (though maybe not with the oil during labour?).
Hot pads (you can use hot wet face washers or cloth nappies) during labour on your nether region might help too.
And I expect that not pushing against your erge - work with your body, don't force it or rush it. Breath, wait, work with your body, breath. Waterbirth, or labouring in the water as your contractions get close and steady and you approach transition.
Let gravity help you - best not to lay on your back or let someone tell you when and for how long to push.
I tore the worst in my labour on my left side on the bed, next in a reclined position in the back, and least when I had my twins on all fours. Anecdotally tearing does seem to be less severe in subsequent labours but position and perenial massage can affect this dramatically, as can avoiding an epidural and therefore limiting your risk of an instrumental delivery.
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