Ultrasound at 8 weeks and 12 weeks?

I'm trying not to be paranoid but it seems like I just keep finding things to worry about! I wanted to see if anyone else experienced this and could calm my craziness. I went in for my first ultrasound at 8 weeks. It was transvaginal and the doctor was pretty quick, but we found the baby with a good heartbeat and even a little movement. Before I left he said he would give me another ultrasound at my next appointment at 12 weeks. I was happy because of course I want to see the baby again! But then I saw another person who has the same ob say he only gave her ultrasounds at 9 and 20 weeks. Anyway, it just started to make me wonder if there was a bad reason for it. Is it normal to check on the baby at 8 and 12? It seems kind of early and I'm just hoping he didn't have a concern that he didn't share with me. This is my first pregnancy with no history of complications or concerns.