What Does Increase In HCG Levels During Pregnancy Indicate?

Hi. I am pregnant -- first blood HCG levels came back at 4500 ( at the time 4 weeks and 5 days). Also had a vaginal sonogram at that appointment and they were able to see a sac. Had a follow up appointment 5 days later -- vaginal ultrasound and blood drawn again. Doctor was able to see the sac and fetal pole -- no heartbeat. He said he wouldn t have expected to see a heartbeat yet. Received a call that night telling me he had bad news -- my HCG levels had dropped to 4000 -- he is expecting me to miscarry. Went back to have blood drawn 4 days later and my levels had gone up to 5400. He believes this small rise is not meaningful in anyway and still believes this is not a viable pregnancy based on these numbers. He is certain I will miscarry and believes I should schedule a D &C. I have no signs of miscarriage -- cramping, bleeding, etc. I have had 4 healthy pregnancies, 2 miscarriages in the past. Both of those miscarriages happened early and I was able to miscarry naturally. Intellectually, I know that the fact that my levels dropped and have not doubled is not a healthy sign. On the other hand I am scouring online and finding so many women who have had similar stories -- levels drop and/or rising slowly to wait it out and end up with a viable pregnancy. My doctor has said that in the over 30 years he has been practicing he has never seen a woman s levels drop and it be viable. Just wondering what your thoughts are? Ectopic pregnancy has been ruled out. Are levels dropping ALWAYS a sure sign of a pending miscarriage? Should I be hopeful at all with this small rise in my levels? Am 42 years old and know that this is my last chance at having another baby so want to make sure we are not being quick to make a decision with what could end up being a viable pregnancy. Any feedback would be appreciated.