The bad part of tanning is the possibility of raising your body temp. I don't think a little sun would hurt but I am really thinking a little. I know tanning lotions and spray tans are fine.
definitely use sunscreen, make sure not to overheat and stay hydrated...
I live at the beach and during beach season I will be in my third trimester. I am wondering if I should avoid the sun or if it's all good. I don't see how a little vitamen d could be bad as long as you make sure not to get too many of those harmful uv rays.