So I had my second ultrasound today and I'm 6+1. My OB saw a second little thing on my ultrasound that looked like a sac but nothing in the middle of it. She wants me to come back in two weeks to see if it's a second baby or just something else such as fluid. Has this happened to anybody else? You saw one baby and one heart beat and you went back to find out that there were two babies? Twins don't run in either side of the family so I'll be really shocked if there are two.