I have had a m/c, 2 girls, and am now 9 wks pregnant again. I didn't get my HCG levels tested with the m/c but I did with the other 3 and I've never had the levels double. I think the first two were pretty similar. I had the levels tested around 7 weeks and they were something like 175,000 and went up to 190,000 two days later. So, nowhere near doubling. The Dr said it was because the higher they get the slower they rise. Even this time I got them tested earlier and at 5wks 1day they were 10,000, and at 5wks 3days 15,000. So, not double again but it didn't worry me, and I have just had a scan that showed everything is fine so far. I definitely wouldn't worry about it xx