High hCG + no yolk sac visualized = ??

Hi all, I am 4w5d and 21 dpo today. I was experiencing bleeding and a fever yesterday and was sent to the ER to rule out ectopic pregnancy. The ER doctor said the fever is likely unrelated, but also said I was probably miscarrying because they could not see a yolk sac on the transvaginal ultrasound. He stated that even though it is very early, he would expect to see a yolk sac with my hCG levels (8,300 at the time of scan).

I'm having another blood test hopefully tomorrow to determine if I have miscarried yet.

I'm curious though, does the hCG level really dictate what is visualized in an ultrasound more than actual length of pregnancy? I know the bleed is not a good sign and I've already accepted the threatened miscarriage diagnosis, but it seems early to call it from an ultrasound.

Note: I don't think there's a chance I ovulated earlier than estimated because I was out of town just hours before that time, and I don't think I ovulated much later because I got my first at home positive at 9 DPO.

Edit: They did visualize the gestational sack, it is not ectopic. They did find two small fibroids but didn't mention if those could be the cause of the bleeding.

Appreciate you all very much!

Update for anyone in the future going through something similar: I had another TV ultrasound today at 7 weeks and they could see the baby and heartbeat clearly. Best wishes to all of you early mommies out there ❤️