I've heard both but a random personal choice I'd say don't because your hair is going to grow so fast you'll have so many roots and by second trimester it's definitely suggested you don't
I was told no bleach but u can dye ur hair after ur second trimester
I asked my doctor when I was 8 weeks and she said it was fine for me to bleach my hair :)
Only if done by a professional or in a well ventilated room and you have no cuts or open sores on your head.