when is the latest to have an ultra sound done?

I had one when my pregnancy was confirmed, another at 19 weeks, and several in the weeks before giving birth because I had preeclampsia and they were keeping an eye on the baby. But as I understand it, there's one around 10-14 weeks and another at 18-20 weeks, and sometimes one at the hospital when you're in labor if your pregnancy is normal. If there are any health concerns or complications, though, I can tell you to expect them as often as every week after week 30.