Thank you, thank you, thank you all!

I am just so excited, I can hardly stand it!
So I'm dying to ask.....about the ultra-sound.....I know they're not reliable in counting pups when there are a few, but if they saw only one, is it most likely that there is only one? Where in there could another be hiding at this stage? I will be having an xray when the time comes, so will know for sure then, but I was just curious on what others thought.