One of the PP's here. My sister had a 10 lb baby. She was (and is again, b*tch) 5'2" and a size 2!!!!!!!!! No epidural, long labor, she had on the small end of a 2nd degree tear and her recovery was just fine. I am 5'7, also was a size 2 (not anymore

) had a 6.5 lb baby, short labor, and also had a 2nd degree tear, though I actually had more stitches than her. We are both in great athletic shape, and both of our doctors told us we'd have big babies based on ultrasounds. So funny -- hers was right, mine was wrong. Her doc pushed a c-section, so she fired him and hired a midwife.
We both had natural, drug free childbirths. I was there for hers, and was amazed that, pushing out a 10 lb baby didn't seem much harder for her than pushing out my pipsqueak.
Moral of the story? It is more than possible for narrow, little women to give birth to a healthy baby and stay in good shape "down there." Sis claims that going natural (which she's the least "crunchy person I know" was what saved her tears -- she just switched position a lot and her midwife did a great job of supporting her perennium.