My daughter was very large. She was 9 lbs & 3 oz. Too big for me to have naturally, and the doctors didn't realize she was that big or I would have had a c-section. I had a lot of problems during labor, and almost ended up dying.
I don't have an answer to your question but would you mind if I asked what caused the fourth degree tear? I didn't know until recently that there was such a thing.