Its completely safe. Your hormones may change the color though. I'd do a test strip first.
I dyed my hair even bleached it before knowing I was expecting and do my roots like every two months and my babies fine. I've heard its safe after the first trimester.
I'm also 19 weeks and talked to my dr about it 2 days ago at my visit. She said a dye that is ammonia free is fine, like the wash out (not permanent) kind. I got an ammonia free permanent dye. They're harder to find but they exist lol.