Vanishing Twin Likelihood?

Charity

Does this look really bad? Ok, so I had my 7 week 3 day ultrasound and the doctor said there were two heartbeats with one at 159 and the other at 131. All he said was one was smaller than the other but I don’t know by how much. Should I be prepared for a vanishing twin? My next ultrasound is one week away from yesterday. My last ultrasound was on Monday.