I dyed my hair around 8 weeks and the color is completely faded. The hormones my body is producing completely rejected the color. All was fine with baby, but be careful! Hair can come out any color it darn well pleases and it might not stay in long at all.
I dye with a rinse every 2 weeks or so. Rinse is only a conditioner so it's perfectly safe!
The book I got from my doctor as well as other online reading say it's safe to dye your hair while pregnant. I keep my hair a very vibrant red and would have continued to dye it but my fiancé asked me not to concerned about the pregnancy. Out of respect for his feelings I haven't.
You can still dye your hair as long as you're in a well ventilated area. Since middle school I've dyed my hair black, I'm a natural brunette but I haven't dyed my hair my whole pregnancy and I'm 34 weeks now. I haven't dyed it because even though I've read online you can, I still don't want to risk it, the chemicals are very strong. Besides, I like my natural hair color, haven't seen it in 8 years !(: