I am so sorry for what you have been through, Diamond.
The genetics of bipolar disorder are very complex. There is not one bp gene--so far. The illness is almost certainly highly multifactorial. Highly.

That said, most big studies show somewhere in the range of 40-70 percent or so inheritability.

My children are my joy. I wish you luck and support you whatever you choose.

I know nothing about borderline stuff and pregnancy.

Hugs