Blighted Ovum or Anembryonic Pregnancy

I went for my first ultrasound and appointment and at ultrasound the technician saw just a gestational sac and no baby so she said it was probably too soon for the baby I was measuring 6 weeks. Went back 5 days later to make sure why I had an empty gestational sac so did another ultrasound and still no baby and no heartbeat my doc said I developed a gestational sac but the fetus never devoloped.