baby in sunny side up position - posterior position

Totally understand your worry, a posterior position at week 37 does raise the chances of a longer labour and more back pain during contractions, but the good news is many babies still rotate on their own before or even during labour, so it's not a done deal. Someone in my mum group mentioned that doing hands-and-knees positions regularly from 37 weeks onwards helped their baby turn before delivery, so that's worth asking your gynae about. The real trade-off to know is that if baby stays sunny side up at delivery, the head fits less neatly through the pelvis, which can mean a prolonged labour, more pressure on your back, and a slightly higher chance of needing assisted delivery or experiencing tearing, but vaginal birth is still very much possible. It's worth having an honest conversation with your OB about what your specific pelvis and baby's position look like closer to your due date, so you can plan together rather than wait and see.