It doesn't happen to everyone. Just some people can't handle the balance because of hormons and their hair doesn't come out like they wanted. My hair dresser told me when she was pregnant with her daughter she bleached hers and it turned grey and blue. But like I said it's not with everyone just some, and if anyone it too worried about it they could always do the test. :)
I bleached my hair and everything turned out the way I wanted as if I wasn't even pregnant
Bleach is really hard to know how it's going to turn out. I mean if you're in a ventalated area dying and everything is okay. But since bleaching and stripping kits are higher on chemicals and amonia it's harder to know how it will turn out while pregnant. They do have a test you can do to try to get an estimate of if it will turn out how you want. (your hairstlyist should know) you put a little on your wrist/arm and behind your ear and leave it for 5 minutes or so. If both are the same color it's less likley for your hair to come out a different color than you expected. I've dyed my hair multiple times while pregnant now, and bubs is just fine. He's actually a little bigger than normal. So yes 100% okay, just at your own risk of it not turning out how you are expecting. Good luck! :)
As long as you are in a well vented area it will be ok.
I have a baby book that says it's ok to do all over highlights so I did it and my baby is perfectly healthy