Well.....do as you like, but remember that there is a definite potential for problems due to lead posioning (I used to work in the lead-acid battery business in EH&S), but also from the percussion of the sound waves. Also remember, if they do enough testing, EVERYTHING is harmful for you and an unborn child.
My wife and I just had a little girl on Dec 22. We used to ride on my vibromatic- Harley Davidson up until the end of month #7. We also rode my Ducati on really twisty roads at up to 3x the speed limit. Both bikes are not good for the baby....weren't necessarily "good" for us, either. When my wife got too big to get on the back of the bike, we started going to an indoor range. We only shot smaller caliber loads, didn't shoot if there were more than two other people shooting besides us, if the baby got to moving too much, she left the range, and she wore a respirator to reduce lead exposure (and washed her hands and changed clothes after shooting).
I know. Lots of you are thinking "Oh, so horrible!". Yeah, well, things that cause more damage to a fetus were avoided throughout the pregnancy.....I quit my band so that my wife and I weren't around cigarette smoke (she always went with me to gigs), BOTH of us quit drinking, vitamins were taken as directed, diets were watched, and all doctor's appointments were met......interestingly, my mom smoked with me and my three sisters, drank, went to the range with my dad, and who knows what else was done. All of us came out fine.......Anyway, our daughter was born 2 1/2 weeks early, was in all safe areas of size and weight, her hearing and sight checked out fine by all of their preliminary tests, and she's healthy as a mule...gaining 33% worth of her birth weight in the first two weeks.
Anyway, my two cents worth.......do as you like, take precautions, understand that there are consequences for EVERYTHING you do, and don't worry too much..........don't forget, using a cell phone can cause cancer, sitting too close to the TV can cause cancer, drinking too much water can cause you to drown, the aluminum in your drink can will cause Alzhiemers, and every time you get in your car, you run the risk of getting into an accident.