HCG levels not doubling

  I am approximately 4.5 weeks pregnant.  Last week I had a brief episode of
  brown spotting, very small amount and some light cramping on one side.  My doctor had me come in for an exam and ultrasound.  The ultrasound confirmed
  me at 4.5 weeks with a gestational sac in the uterus, probably ruling out
  an ectopic pregancy.  My concern is that my HCG levels have not been doubling.  1/15/99 it was 987, then 1/17 it was 1007, then 1/19 it was 1400.  I have had another higher level ultrasound, with nothing found to
  indicate an ectopic pregnancy.  What could be happening?  What is the
  likelihood that I will have a miscarrage (miscarriage).  I have had 2 healthy pregnancies
  previously.  Please advise.
Dear Ruth:
Pregnancy begins with the formation of the early placenta, then the fetal sac, and finally the embryo. The hCG is produced by the placental tissue. We do not understand how the placenta knows if the fetal tissue is forming normally: we presume there is a signalling system. If the signals are appropriate, placental growth, which we guage by the hCG levels, is stimulated. If the signals are not normal, placental growth begins to slow and eventually stops.
An hCG level that does not double every 2-3 days reflects slowed placental growth and this correlates strongly with abnormal development.
My crystal ball is very cloudy for predicting pregnancy outcomes. Falling hCG levels are a bady sign; decreased rate of rise is a warning sign. An ultrasound study between 6 and 7 weeks will be the definte test to know if fetal development and fetal heart motion are present to reassure that the hCG was misleading or whether is is a "blighted ovum" wherein the embryo fails to develop.
Miscarriage occurs to 1/3 pregnancies: past history of normal pregnancy does not change this statistic.
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This information is provided for education purposes only and is not a medical consultation. If you have specific questions, please contact your physician.