Blighted ovum?

For those of you that had a blighted ovum what we're your hcg levels like? My levels on the 23rd were 8100 and on the 26th they were 21000. Someone told me that hcg rises quickly when it's a blighted ovum. Is that true? I go in Tuesday for a follow up ultrasound. My doctor said there's a small chance I have a blighted ovum since we didn't see anything on the ultrasound but the gestational sac or I could just be really early. He seemed happy with my levels but then when someone told me that blighted ovums have faster rising levels it freaked me out even more. Doctor thinks when we did the ultrasound I was anywhere between 4w6d and 5w4d. Thanks in advance for any info given! :)