I had one yesterday morning at 4w5d. There is for sure one sac in there, but he couldn't confirm or rule out a second one, there is a shadow that could definitely be a second sac, or could be just shadow. I have my next scan on Jan 4th. I will be almost 8 weeks then and it should be much more clear. My dr is still pretty convinced its two though, my HCG went from 50 to 180 in 48 hours, then from 180 to over 1200 in four days. The numbers aren't super high for how far along I am, but they are tripling every 48 hours instead of doubling, so fingers crossed!! I would love twins!