Possible twins?

Today I had my first ultrasound, but still a bit early (only between 4&6 weeks.. While looking at the ultrasound my Dr said that there might be twins because there are two spots. It could just be fluid too, she said. I haven't set my hopes too high. Anyone seen something this early and then ended up with twins? I have another ultrasound next Wednesday as well to check heartbeat and stuff... it's gonna be a long week.