No fetal pole?

Hi guys, I went in for my first ultrasound. They told me that I was 6w4d based on my gestural sac however I marked myself I little earlier based on when I got my first + pregnancy test.

The ultrasound showed a yolk sac but no fetal pole. They said that it is probably too early but when I got home and started googling, I found that a fetal pole is very commonly seen at 6 and a half weeks? They said to come back in for another US in a week or two.

Has anyone experienced this? Have they got a heart beat when they have went back or are the doctors just waiting to offically deem this an anembryonic miscarriage?

Thanks guys!