14 weeks pregnant and scan showed empty uterus

Hi guys,
I am 14 weeks pregnant with twins. I went in for my scan yesterday and the sonographer was perplexed as he did not see anything but an enlarged empty uterus. He rang through to the hospital and got my last scan that was done there 3 weeks ago. He looked at that one that showed the twins and looked at this recent one. He said I am really sorry but I don't know whats happened. I was in so much shock and soon the tears came. My midwife not long called after and I went straight to my doctors. I have to take a blood test to check my pregnancy hormones before I go back to my doctor. He said its not 100% percent I have miscarried. My uterus is enlarged when he felt it and I am showing along with all the other pregnancy symptoms still. Is it possible that they are just hiding?