need hcg level help

j
8/26-   8wks pregnant 
Hcg 110,006 6wk embryo w/hb
9/9 -    10 wks pregnant 
Hcg 1,000 6wk embryo no heartbeat
9/22-    2 wks after abortion pill for mmc
Hcg 990 
Only dropped 10 points from 9/9 to 9/22. Any idea why there was such a small drop?