Twins?.

Okay, so I had to go to the hospital last Thursday for an ultrasound ordered by my doctor, the tech wouldn't give me any information. Anyways, when I got up to use the restroom & get dressed I glanced at the screen & I saw '5w 4D & 6W 4D' could that mean twins? I'm so confused & if it is twins why would one be a week behind? Would that baby be okay still? I have an appointment tomorrow afternoon for my results but the thought just popped up in my head a few minutes ago.. any input would be greatly appreciated.