It penetrates through your scalp and the "little" bit of chemicals can and do get in your blood stream. First trimester is the most crucial part of development. Don't get me wrong, I've done my hair about 4 Times since I've been pregnant but after my First trimester:) just be careful and put baby first, and like she said, ammonia free dye is always the best route! :) I know roots are annoying. Just hang in there.
It isn't correct to say it's unsafe to dye your hair in the first trimester. Though professionals believe that none or little of the chemicals get absorbed into the skin, not enough research has been done to know if it's safe or not. So doctors recommend waiting until the second trimester to dye hair. I personally started dying my hair again toward the end of my first trimester, and I used ammonia free dye.
No. Wait til your second trimester.