Just want to say that although the whole unknown factor of labour & birth is scary, please don't worry about something that probably won't happen. I birthed a 9 lb posterior baby with a not so small head & I did not tear at all. So it's definitely not a given.
Even if you do tear, you may not even know at the time. There is just so much going on!
Educate yourself on birthing positions & active birthing - our bodies are amazing! Good luck!