Understanding Slow HCG Rise in Early Pregnancy: What to Expect

Question
-------------------------I figure from conception that I am four weeks but by my LMP, it shows six weeks. My level of 371 is within the range for a four week pregnancy and not the six week range. My doctor will not due a sonogram until my levels are at 1500 and that could take forever with the way my levels are rising. Is there a possiblity that I am only four weeks instead of the six weeks that the wheels estimates me to be?
Followup To
Question -
I am 31 years of age. I have one 11 year old girl. LMP 02/11/2004.

On March 15th my beta hcg level was 38, on the 17th it was 146 on the 24th it was 371. My doctor has instructed me that there is a possiblity of a tubal pregnancy or miscarriage, but I feel very pregnant with no symptoms of either.

Can I have a high risk pregnancy due to hcg levels not doubling every two-three days?
Answer -
YOu may be off on your dates and it may be a very, very, early pregnancy; or you may, indeed, have the beginning of a miscarriage. However, if you are not seeing any bleeding or having any cramping, it is not likely that you are having a miscarriage. If your period started on February 11, you are now 6 weeks 3 days gestational age. A sonogram at this time should show a fetus, a gestational sac, and a fetal heartbeat. Take a sonogram and it will confirm or rule out a viable intrauterine pregnancy. (If it shows nothing in the uterus, it may show evidence of something in the tube). In any event, it will reassure you one way or the other. (By the way, the "rule" of HCG doubling every 48 hours is not written in stone.)

Answer
We date the pregnancy based on the first day of your last period, not on your date of conception. Based on the first day of your last period, you are now 6 weeks 3 days. A sonogram at 5-6 weeks will only show an empty gestational sac. A sonogram at 6-7 weeks will show a fetus and a fetal heartbeat. Unless you were in error about the first day of your last period, it does not always matter what the HCG value shows. If you are not having symptoms of a miscarriage, you can safely wait a few more weeks, take another HCG to see if it is rising and then do a sonogram later. However, the sonogram will resolve the issue.