I was told bleaching is perfectly fine as long as its well ventilated. I know a ton of people who bleached their hair & the doctor said it was fine. my Dr said I could bleach my teeth so hair is perfectly fine.
I would check in with your doctor first, and go to a stylist you trust. I went in to get my roots bleached over again and my stylist recommended that we do foils instead so that the color wouldn't QUITE touch my scalp. She said it was more for my comfort because she has colored/bleached hair with pregnant women before (and gotten it done herself last year when she was pregnant) and color seems to burn your scalp a lot worse while you're pregnant than it normally would! So just be cautious, and maybe go with foils instead of an all over color 😉