Why is it so hard to make sense of your HCG levels ?

HCG ( also known as beta HCG or just beta) is a very special molecule. It's unique in that it's produced only by the placenta ( very very rarely, it's also produced by some ovarian and testicular tumours). This means that for all practical purposes, it's found only in pregnant women and is therefore a very good marker for pregnancy.

Since the HCG is produced by the placenta, the levels of HCG rise as the pregnancy develops, and there is very good correlation between the health of the pregnancy and the HCG level for the first few weeks of the pregnancy ( from about week 4 - week 7, as calculated from the LMP, last menstrual period).

However , it can be hard to make sense of your HCG blood levels. Let's look at some of the pitfalls in monitoring your beta levels.

Most patients naively assume that a beta of more than 1 mIU/ml means that it's positive and that they are pregnant. This is not true. The new kits are very sensitive , and even men can have levels of upto 10. This means that a level of less than 10 mIU/ml should be considered to be negative.

Secondly, remember that the HCG is produced by the placenta and not by the fetus. This means that the HCG levels may rise , even if the pregnancy is not viable ( such as an anembryonic pregnancy or a missed abortion).

Since HCG levels rises exponentially, there is a very very wide range of normal. This is why it's very hard to interpret just one level in isolation . It's important to check at least 2 levels at least 48 hours apart to determine the trend . In a healthy pregnancy, the levels should double every 48 - 72 hours. If they do not do so, this suggests your pregnancy may not be healthy.

It's not possible to determine whether the pregnancy is single or multiple based only on the HCG level. While it's true that HCG levels are higher in multiple pregnancies than in singletons, because there is so much overlap, you cannot jump to any conclusions based on the HCG level alone. This is why it's important to interpret the HCG level in conjunction with vaginal ultrasound scanning results.

Also, normal ranges can vary widely from lab to lab, because they use different kits. This is why it is important to check your HCG level from the same lab each time !

Finally, HCG levels are useful only in the first 7 weeks of pregnancy. After this, ultrasound scans are far more useful because they provide much more information about the location of the pregnancy; how many sacs there are; and whether the fetus is growing or not.

NORMAL SINGLE PREGNANCIES

Day after HCG or LH ( DPO)	Average mIU/ml	High mIU/ml	Low mIU/ml	#
14	48	119	17	12
15	59	147	17	18
16	95	223	33	23
17	132	429	17	21
18	292	758	70	19
19	303	514	111	23
20	522	1690	135	13
21	1061	4130	324	12
22	1287	3279	185	22
23	2034	4660	506	13
24	2637	10000	540	16

The information in the table above is part of a study carried out by Dr. Sherbahn