Understanding a Slow Fetal Heartbeat: Causes & What to Expect

Question
Hello, I'm 28 and have a 21 month old son.  My LMP was 12/31/06 and I had a positive pregnancy test on 1/28/06.  I went to the doctor at 6 wks 6 days and had an ultrasound.  The P.A. indicated that the baby was measuring 4-5 days smaller than my calculated date and it seemed too early to see a heartbeat.  This did not seem odd as my cycle was generally 30-31 days.  I went back ten days later at 8wks 2days and was told that the baby had grown but now measured two weeks smaller than my calculated date and there was a heartbeat but that it was slower than it should be.  I guess I am asking what are my chances for miscarriage?  I have had no spotting or cramps and am experiencing the nausea, sore breasts and fatigue associated with early pregnancy.  I have another ultrasound scheduled in a few days, should I expect not to see a heartbeat at all this time?  

Answer
As long as you are not having bleeding and cramps, it is unlikely that you are miscarrying. However, after 6 weeks gestational age (from the first day of your last period) the FH should be 120-160BBM and there should be adequate growth of the fetus. I would take two blood tests for pregnancy (Beta HCG) 48 hours apart. If there is a doubling of the results in 48 hours, it indicates a viable pregnancy. If there is a halving of the results in 48 hours, it indicates a miscarriage. I would repeat the sonogram at 10-12 weeks gestation and see if there has been adequate growth of the fetus. Don't give up hope at this point.