Well the short answer is we still don't know. I've stumped everyone from the radiographer to the gyno consultant!

We have 4 alternatives, none of which completely fit:
Molar pregnancy
Ectopic
Miscarriage that hasn't come away yet
Viable

I have no pain and have had no spotting since last week. My levels last Tuesday were 1100, on Thursday they were 640 but now they're up to 1680. That's not high enough for molar, but there are dark bodies in the uterus (could also be clots, which isn't necessarily bad). The rise in HCG points away from miscarriage. The lack of pain points away from ectopic. But they can't find a gestational sac, so that points away from a viable pregnancy.

I have to have another scan on Friday and more blood tests to see what my HCG levels are doing. They were initially going to give me a D&C today but they don't want to do that if there's any chance of viable pregnancy.

So I'm back where I started - any pain or bleeding and straight to emergency again!