Does anyone know just how accurate those HCG levels are? Has anyone had a level consistent with a certain week, but it turned out (via ultrasound or something) that it was really a couple weeks off?

I was in the ER with some pains when I found out that I was 3 weeks pregnant. My HCG levels were at 33. By 6 weeks they had gone all the way up to 15,000, which I have been told that was normal and can vary person to person. The HCG levels in your blood are supposed to be VERY accurrate, more accurrate than the urine test. Hope this helped.