Blighted Ovum: Understanding Early Pregnancy Ultrasound Results

Question
I had an ultrasound this past friday at 6 weeks 5 days, and the only thing there was a gestational sac.  They are having me come in on this coming wednesday when I will be 7 weeks 3 days to check again, and if it is still just the sac, then it will be diagnosed a blighted ovum.  What are the chances of a yolk sac and heartbeat developing this late?  Is it possible at all that I will see some development on wednesday and not have to face a miscarriage?

Answer
Dear Jennifer,

I also had a similar situation last year, and it is always frightening to hear that there might be something wrong.  Just stay positive during this difficult waiting period.  There is always a possibility that the heartbeat will be visible, however there is usually yolk sac visible by 6 weeks.  Of course there are cases where it was not visible on ultrasound due to the skill of the technician, the equipment or other factors.  If there is still no visible heartbeat by 7 weeks, it is likely a miscarriage.  All the best and think positive,

Sarah