Went for an 8 week vaginal ultrasound after spotting doctor found no baby in sac my hcg levels were 21000 i will be going back in three days to re tes?

Blighted Ovum: Unfortunately, this is one of the most common causes of miscarriage. During the very early stages of pregnancy, some cells become the fetus and others the placenta and membranes. When this differentiation doesn't occur, the sac is empty, as no fetus ever developed. More than likely, you will need a d & c. So sorry.

Follow up imperative: You have either had a complete miscarriage, or more seriously an ectopic pregnancy. You need to follow-up with your doctor without fail. He/she will re-check b-hcg level, and probably order another ultrasound. With your b-hcg levels that high, a fetus should be seen in the uterus. Consultation with your ob/gyn is mandatory. Go to er for any abdominal pain, or significant vaginal bleeding.