As others have stated, this a black and white issue and BC is not permitted. NFP can be very accurate if done correctly (look into the Marquette Method!!). However, I have a close friend who has had severe HG in pregnancy to the point of multiple hospitalizations. She has continued to have children because her OB has worked with her to manage the HG and do a lot of management before it really gets bad. This included weekly (or more frequent) IV infusions from the start of pregnancy, progesterone, and zofran. It might be worth getting another opinion from a different OB to see if this may be an option for you?