no fetal pole detected

I just got back from my ultrasound. Should be 7wks today. Saw gestational sac, but no heartbeat and no fetal pole. 
I guess I could be earlier than 7 weeks, but first day of last period was 1/4 and first positive pee test was 2/1. 
I'm thinking blighted ovum? Anyone else not show anything at 7wks and end up turning out okay?