The biggest thing for me is lack of tiredness. If I have disrupted sleep one night and I'm not tired the next day then I watch very closely for other signs. Often it is harmless and resolves but I'd rather be over vigilant and ready with some meds to reset my sleep patterns cos the lack of sleep drives the mania. (I used to use low dose seroquel for my sleep and bump it up to high if it continues past a couple of days, not sure if I can take it while pregnant though)
Some other things are if I'm feeling really motivated to do things that I normally find difficult, if I'm getting impatient with things and people or I'm seeing special importance or meaning in things. Again sometimes these are false alarms but they are just signs to watch out and be a bit more careful.
Hope you can find your early warning signs and tricks to prevent the manias.