Has anyone had their hair turn gray while pregnant? Does it change back later, or is it a lost cause?

5+ years ago I was pregnant (miscarriage) and my blonde hair did turn darker. Since then I have done highlights to even out the coloring. Now I am pregnant again (20 weeks) and last night I found a patch of gray hair, which is of course in a pretty obvious spot. I'm 28, so it seems a bit early for me to be going gray, so I'm chalking it up to pregnancy. Has anyone else had this? Anything I can do about it? I'm going to guess that highlights aren't really going to cover it up ....