No fetal pole?

It should be about eight weeks pregnant and I went in for my first ultrasound today. I found a sack and a yoke but no fetal pole. My doctor wants me to come back into weeks to see if it develops or if we have to terminate. Has anyone ever had this issue and it ends up developing or will it always end up in a miscarriage? I'm not sure how I feel about all this right now I'm little sad but also little hopeful that it will turn out good.