Blighted ovum

Wont know for sure until Wednesday but my first two ultrasounds didnt go so well as the sack was empty both times. First time we went we thought we were seven weeks and told us we were about five and a half and then went back two weeks later and was only measuring six and there was still no fetal pole or heartbeat.. have to go back in a few days for another ultrasound but thinking it may be a blighted ovum. However my hcg levels were in the 34,000’s when they checked them this week.. is that normal for a blighted ovum ? Preparing for the worst, we have been through a miscarriage once before... just confused about all of it.