Egg yolk, no embryo on ultrasound

Hey ladies!
I thought I was 7 weeks and 4 days based on the first day of my last period. 
My first doctors visit was going great this evening until the ultrasound. The tech found an egg yolk, but no embryo inside. My doctor said this was odd for 7 weeks and ordered more Bloodwork in a couple of days. 
In the meantime, has anyone else experienced a similar situation with positive results?
If I did miscarry, would an egg yolk still be present? 
Thanks in advance!