at 15dpo (on IUI number 7 coincidentally!) my HCG was 26. it doubled in about 2.5 days. sounds similar to what is happening to you. that low starting level is now a very noisy 6.5month old!

the starting number doesn't matter - it's how it climbs. generally they say doubling in 48hours BUT,i've done a lot of reading (as you do in these circs) and that is what they HOPE happens - it's not a rule. many women have levels that rise as little as 66% in 48hours and still go on to have successful pregnancies

with an IUI, conception date isn't guaranteed. we assumed it would happen on the wednesday (day after IUI) - from all the scans we had, it didn't happen til the saturday or sunday - which makes sense with us having a girl!

HTH

BG