Answer: At this point, doctors remain unsure whether or not bleaching your teeth is free of harm during pregnancy. Doctors do say that the oxidative process caused by bleaching has been known to harm tissues and cells, but it is unclear how this translates to pregnancy.
It is for this reason that doctors recommend that you wait until after the pregnancy and even after you have finished breastfeeding before you bleach your teeth. This applies whether you are having a professional dental procedure or using over-the-counter whitening products.
In truth, there is just too little information about bleaching your teeth while you are pregnant to determine its safety.