Hi Claire, is this your first pregnancy? it is possible that your having twins as a larger tummy is a sign but the only way to find out is with a scan. Get in touch with a midwife and tell her that your concerned. Also, in the early stages of pregnancy everything starts moving around and can make your tummy a lot rounder. With my first, second and third pregnancy, you could see quite clearly that I was pregnant at 8-9 weeks, a pharmacist refused to sell me any vicks sinex when I was 8 weeks because I was pregnant, I was mortified, I did not think it was that obvious. The mid-wife thought I could be having twins too but there was only 1. I hope this helps, Nicola x