Best of luck to everyone. This really is a tough time.
I found a site with HCG statistics based on single and twin pregnancies: https://www.betabase.info/index.html
You can calculate your doubling time when you get your results 48 hours apart. Misspriss, I hope they are taking two HCG draws 48 hours apart, otherwise your levels probably won't tell you much. With my first two miscarriages, my levels were slow to rise and not doubling in 48 hours, and I was told to expect the worst. With my daughter, my levels doubled in 28 hours(!!) and this time my levels are doubling in 30 hours. I am hopeful for that, but still worried about the potential for a blighted ovum. Bleh.