There is no conclusive studies which shows whether it is safe or unsafe (as it is unethical to test these things on pregnant women) however, studies have shown that some potentially harmful ingredients (cant remember which ones - maybe ammonia??) have shown up in non-pregnant womens urine 4 hours after colouring hair so some people do think that it is unsafe. In saying that, my Ob told me it was safe after 12 weeks at which time I started colouring my hair and have done so several times in the past 20 weeks without any concerns.