D.W.
Sunlight is good to help your body produce vitamin D naturally.
However, during pregnancy there are some risks it's best just to avoid. Your goal should be keeping your child as safe as possible while you're pregnant, and I don't think that's possible with the use of a tanning bed or a self-tanning product.
I'd highly recommend asking your OB. None of us are physicians, and we can't tell you, for sure, that it's OK to do anything to help you tan during the second half of your pregnancy. Tanning beds create UV light that can be dangerous, and self tanners may contain chemicals that are dangerous to the baby.
Here's one article I found on BabyCenter. I'd recommend reading and discussing with your OB.
http://www.babycenter.com/404_is-it-safe-to-use-self-tann...
I know, too well, that life can take an unexpected turn. My daughter was 10.5 weeks old when I was diagnosed with cancer. We don't know what caused it, but I had a 2 year-old and an infant, a full-time job, and 5 months of chemo ahead of me. Luckily, my children were born healthy.
Based upon my experiences (and my decade long career in the pharmaceutical industry), I'd say it's just not worth the risk until you've had a chance to speak with your OB about it.
Good luck.