Ultrasound no yolk sac

Kh

I went in for an early ultrasound on what I thought was 6w3d. However I don’t ovulate on CD 14 but later. All that we visualized on ultrasound was a gestational sac measuring 8 mm or 5w3d. My Hcg is still increasing and was 7900.

My concern is from what I’m reading a yolk sac should be visible by now. I’m scheduled for another ultrasound a week from tomorrow. Does anyone have a similar experience? I’m worried about a blighted ovum.