Apparently in your second tri is the safest and do it in a well ventilated area. Ammonia free should be fine anyway. Also hairdresser is fine just as long as they don't put dye directly on your scalp.

I did all through my pregnancy..
Well ventilated area n I use garnia oila... Oil base.. No ammonia

I did through our I know some people say omg it goes through your skin it’ll harm the baby blah blah but I’m a professional and have been doing it 10 years and pregnant woman do it all the time it’s perfectly safe just make sure u do it outside or with windows open as home dyes tend to give off a very strong smell