Congratulations on pregnancy.
I guess my bipolar symptoms started before/during my second pregnancy, but I was not diagnosed yet back then. I had two pregnancies one after another and it set my bipolar symptoms on. The best thing probably was that I did not know about being bipolar back then - less you know, less you worry.
I was hospitalised in womans hospital as I now think during manic phase when I wasn't sleeping and was so active that it led to uterine acitvity, felt like abdominal pain. Had intravenous magnesium to calm that down. Did help.
I would suggest avoiding as much as you can all your trigers, taking multivitamins, fish oil. Check your vitamin D levels, at least for me it was low, supplementing helped my moods. Try to rest and sleep as much as you can.
Take care, all my best wishes