6 wk ultrasound but no fetal pole

I had my first ultrasound & I should be 6 wks & 3 days, but they didn't see a fetal pole- only a sac & yolk. Did anyone else have this & everything turn out ok? I know this is still considered very early (the only reason I had it done was because of a previous miscarriage), but I've seen so many women say they could hear a heartbeat at this stage & even a few days earlier. I'm just nervous it could be a blighted ovum & I don't know if I'm prepared to go through all of that. :( thanks in advance for your replies.