Hi-
I'm on my second pregnancy and my second OB/Gyn and have been told that it's okay to color my hair for both pregnancies, by both OB's.
My colorist uses Aveda products that are, theoretically, safer due to their "natural" ingredients. To be honest, I take this information with a grain of salt. It may well be true, but I don't know that that's really the case.
Since you're still in the 1st trimester it might be a good idea to give your OB's office a ring, just to make sure that it's okay to color in the early stages of pregnancy. Also, I think that your previous respondent, who said you might need to be concerned that pregnancy hormones might impact how your hair reacts to the coloring chemicals is correct, too. Maybe your colorist could do a test strand to make sure you don't come out bright orange...
Good luck!
M.