I have always had low blood pressure and it seems to stay the same during pregnancy.
Fainting and dizzyness are a problem for me, so try not to stand still for too long, for example, if you are in a queue waiting for something move from side to side to prevent getting dizzy. And if you do feel dizzyness coming on then sit down and put your head down, or start walking and see if that helps. I don't know of any problems to bubs due to low blood pressure, just more of a yucky feeling for mum really!
Mine is usually around 100/60 lately, so not too bad.