While you can whiten your teeth during pregnancy, you might want to think about if you really need to. There’s no substantial evidence that teeth whitening is dangerous for your baby, but there also isn’t an abundance of evidence that proves it’s safe. Most obstetrical and dental professional organizations recommend avoiding cosmetic procedures while pregnant.
The main ingredient in whitening agents is hydrogen peroxide (or something that breaks down to hydrogen peroxide, like carbamide peroxide). Hydrogen peroxide for this purpose is considered safe, with the main side effect being tooth sensitivity. Regardless, it’s probably best during pregnancy to just practice good dental hygiene by brushing twice daily, flossing daily, and seeing your dentist every six months for a cleaning.