T.S.
Hi,
I highlighted my hair and colored them once when i was pregnant with my now 13 month old son. My OBGYN had no problems with me to get it done as long as i got it done after the first tri-mester. The only thing i did avoid was the fumes(sat with the window open) and i asked my stylist to leave the application for the minimum possible time . My sis-in-law,sister both did the same thing when they were pregnant with thier kids respectively.I only colored them once and the rest of my pregnancy used ammonia free hair color enhancing shampoos.Hope this helps.
Go with whatever makes you comfortable. Good luck with everything!