Is it safe to ride in a tractor trailer while pregnant?

Certainly, although it might not be the ideal place to be, especially if you're due anytime soon. Labour could start when you're in the middle of nowhere, Montana, for instance, and that could put you in a bit of an awkward spot.

There's a lot of other considerations you might want to dwell on, as well. The bunks in the sleeper berths tend to be quite small. If you have a two bunk sleeper, one of those bunks is going to require a climb to get up there - if the driver isn't giving up the bottom bunk, you need to think about whether or not you really want to climb up onto such a bunk. Or, if you sleep in shifts, you need to consider whether or not you'll really want to be sleeping in the bunk while that vehicle is in motion. Most trucks have restraints for a sleeping passenger, but they can be a bit uncomfortable, and, if you don't use them, you could risk falling out of the bunk if that truck has to come to a sudden stop. If you do fall out of the bunk, a bad landing could put the baby you carry in a very bad way.

All in all, it's no more dangerous than riding in any other vehicle while pregnant, but I tend to be of the opinion that it's a really bad idea.