According to the medical research studies it certainly can be.
In my case it is: My grandmother was bipolar, my sister is cyclothymic (mild form), & my cousin has bipolar for starters.
On the other hand neither of my parents or my other sister or brother has any problems.
Depending of the type of Bipolar disorder that you have you may end up needing to see someone about it. Eight months pregnant may not be the best time, but if your highs and lows seem to get progressively worse, or you are unable to keep a job or for instance it may be time to get some help...