Due 12/10 what to expect at ultrasound

This is my third baby but it's been 8 years! 
We are due 12/10 And are having an ultrasound on Monday. I will be 5 weeks 3 days. Should there be a sac and a baby visible at this point? I want to be prepared. And if there were twins, would it show already at the ultrasound. Thanks in advance ladies!