Is there any way of knowing how big my baby will be before it's born?

I asked my doctor, and she said there was really no way of knowing until the baby is born. She says they give 3rd trimester ultrasound only if they feel the baby is measuring to big or too small. I just started to gain weight and I am 7 months. I put on 5 pounds so far, I just think that it is strange with all the technology we have today, more effort is not put into finding out the baby's size. A co-worker at work says her baby was so big, it got stuck in her pelvis, and they had to give her an episiotomy, that consequently tore her rectum. Her doctor then admitted she probably should have had a c-section. I am scared out of my mind-what if I have a 10 lb baby. Will they expect me to squeeze that out lly I have heard of baby's getting stuck in the c and needing an emergency c-section. How common is this?