Pregnant why would i need to see an obstetrician?

i am 11 weeks pregnant with my third child i had no problems with those pregnacies, my blood pressure yesterday was low 80/50, my bmi was alittle over at 26 and i do suffer from anxiety, but it says on my letters that you only get referred to an obstetrician if there is a problem can it be because of any of these problems i am starting to worry