What do you think the possiblity of twins is?

i am in my 2nd pregnancy and the doctor said i was a liltte bigger then i should be and i hd a complete sonogram 3 weeks ago to check for measurements an stuff like that.. well when i went to the doctors to see how the images were they said i have to go back to do a whole other sonogram when i asked if everything was okay they said oh yes everything looks completely normal but we want to do another one. Do you think i might have twins ...note there are no twins in my family but there are 3 sets os twins on my hubbys grandmaothers side.