What should normal hCG levels be at 5.5-6 weeks? Should the levels be doubling every 48 hours? My wife's levels on the last three tests were 244, 478 and 680.

J.S.

There is little information that can be gained from the absolute value of a single hCG test. We can make a few generalizations: Levels over 2,000 miu/ml should be associated with a gestational sac that can be seen on transvaginal ultrasound. Levels over 13,000-18,000 miu/ml often indicate that a fetal heartbeat will be seen. With multiple births, the values tend to be higher.

One reason the absolute numbers are not very helpful is that levels can vary over 100 percent depending on the lab that is processing the test and the exact testing method used. As a physician, I find this discrepancy quite frustrating. I have had repeated problems after sending blood samples to various laboratories as directed by the patients' insurance companies, and after some unfortunate alarms over seemingly low levels, I have learned never to make any decisions based on a single anomalous value.

hCG testing is often repeated at 48-hour intervals. A rise of 60 percent or more usually indicates things are progressing normally. This certainly does not rule out the possibility of a miscarriage at some later time. Once the levels are above 20,000 miu/ml the rate of rise slows, and the hCG would no longer be the most appropriate way to evaluate the pregnancy. At that point, the transvaginal ultrasound is a more appropriate tool to follow the pregnancy.

If the rise is less than 60 percent -- and all blood was processed in the same lab using the same method -- there is actually little we can do. There is no way to intervene and change the outcome of a pregnancy destined to miscarry. Progesterone, bedrest and other suggested measures may provide reassurance that something is being done, but these steps really don't prevent miscarriage.

But all is not lost when a bad result is noted. Only when repeated values show a poor rise will I get concerned. We have all seen normal pregnancies proceed even after repeated values that suggest reason for concern. Medical diagnosis and decision-making should rarely be based on a single piece of information. Only by combining laboratory findings, symptoms, physical signs and ultrasound examinations can I attempt to make a decision.