Can loud noises effect pregnant women?

I can only relate my personal experiences. We have two two-wheel drive pulling trucks that we compete with on the Grand National Truck and Tractor Pulling Circuit. I have grown up around farming and tractor pulling all of my life. I met my husband at a tractor pull and I know start the engines of the trucks. The trucks have an injected motor (very, very loud) and run on methane gas. The best way to describe these engines are--they are like the engines you would see drag racers use on T.V. Well I was due in September, so needless to say I started the engines my entire pregnancy and was around loud noises otherwise for about all day every weekend....Our last pull was when I was 37 1/2 weeks pregnant. I would ask my doctor this question a lot. He said it was fine because the baby is so well protected inside. After having the baby it was the test I would always make sure was administered and I would ask everyone that came in for the results. Everything was fine. My son is now 20 months old and loves the loud noise and isn't afraid of it and he loves tractors on the farm and going to tractor pulls. he uses the ear muffs now. you will hear that a lawn mower is too loud and decibles are too high. Well what I was around was about 100 times louder.