Widdly I was worried about this too, but Mason came out ok at 7lb 8oz and Angus literally fell out LOL.

It's only natural to have some fears and hearing of others that have had problems will only make you stress more.
What about my best friend who popped out 12lb + babies with only a small tear each time!

Talk to your OB or midwife about how you are feeling. I hope that they can put your mind at ease.