Lost twin?

I am 6w2d w/ twins today. Last week I had bleeding and went to the hospital. They found both sacs. One measure perfectly at 11mm. Baby A measured small at 5mm. Three days later our doctor did another ultrasound and found both gestation sacs with yolk sacs and registered baby B heartbeat at 117 and she said baby A was still a little small but she could almost guarantee that A would finish catching up quickly. Today we went in (three days later) and a different doctor said that B is completely missing. And that A is showing no fetal pole. He is being hopeful A will catch up but said to count B out. Has anyone else had this happen? How did it end? We had a twin blighted ovum back in March/April and we are praying we are not headed back down the almost same road again..