Drop in hcg levels after 4 weeks of pregnancy

Patient: Hi, went for ultra sound on the 14.3.2011, could only see a very tiny dot but had my ovaries and tubes checked and everything was okay, they said was approx 4 weeks pregnant, when i got the blood tests results confirmed my hcg levels showed approx 4 weeks, on the 21.03.2011 did another hcg check which my dr has advised the level has dropped but not by how much. I need to go back for more blood tests, everything i have researched has shown that a drop in hcg levels equals miscarriage or eptopic pregnancy. Nothing showed up on the ultra sound in my tubes and i have had no signs of a miscariage, could there be another reason for the drop or should i be expecting the worst?

Doctor: Certainly in most cases a drop in HCG levels during the first trimester but especially between 3 and 12 weeks might be g enerally caused by a non viable pregnancy ending in a miscarriage.HCG levels should be doubling every 48 hours and only stabilize or drop after week 12. I would suggest you to keep following with your ObGyn for a more detailed evaluation. I wish you the best.