So my doctor just called

Cassie • Having our third, due April 2016!
And asked me if the ultrasound lady discussed anything with me. I said no. Then says there looked to be a second yolk sac. Said one baby looked great obviously but there may be no fetal pole with the other. Going back in a week for another ultrasound. What should I make of this?? What are the chances I could have twins? Or worse lose both of them?