What Does Absence Of Fetal Pole And Heartbeat During Pregnancy Indicate?

Hi, I am 5 weeks and 6 days pregnant through a frozen embryo transfer. I went in for light bright red spotting that has now stopped. They found that I have two gestational sacs and yolk sacs but not a heartbeat or a fetal pole as of yet. The ER doctor came in and stated that he should see a fetal pole now. I am measuring less than 5 weeks and 6 days on the ultrasound as well? I though this could be from the timing of the frozen embryo transfer to implantation?