How to best help my son's girlfriend who is bi-polar and pregnant.?

Without going into great detail, I was wondering if someone could tell me if pregnancy exacerbates the bi-polar condition? And, can you still take your medicines while pregnant? In general, what medicine is prescribed for bi-polar? My son's girlfriend is pregnant (unplanned) and is extremely depressed and volatile. She gets into explosive moods as well as threatens suicide. She lives with us and I'm not sure how to best help her and my son. Is treating her with kid gloves the best angle? Minimizing her stress??? She doesn't want to go home, but, I don't have any experience with bi-polar. My son is being worn thin by it all. He fears for the baby and wants to make sure the baby is alright and protected. Any suggestions or first-hand experience would be greatly appreciated...