Honestly it depends on the type of concert. The last concert I went to was the foo fighters. We had floor tickets no seats standing room only and we were crazy close to the stage. People drinking fighting and trying to start mosh pits. So I definitely would go to another concert like that pregnant. Check with your doctor if you are concerned about the noise levels.
I went to a godsmack and staid concert when I was 8 months pregnant with my daughter and everything was fine. I also saw other pregnant women there as well.