What is being tested?

hCG is a protein hormone produced in the placenta of a pregnant woman. A pregnancy test is a specific blood or urine test that can detect hCG and confirm pregnancy. This hormone can be detected by a blood test as early as one week after conception or by a urine test at around the time of the first missed menstrual period.

hCG production doubles about every 48 hours for the first month of a pregnancy and continues to rise steadily, until about 10-12 weeks when levels drop until about the 20 week mark, and then continue largely the same until term.

It is important to note that there is a wide range of hCG levels between individuals, but this trend appears to be relatively constant. Estimates of gestational age are difficult to do using hCG due to this wide variation between individuals, so ultrasound investigations are used to check pregnancy duration. hCG is no longer detectable a few weeks after delivery.

During the early weeks of pregnancy, hCG is important in maintaining function of the corpus luteum (the mass of cells that forms from a mature egg into the developing embryo).

If something goes wrong with the pregnancy, the level of hCG may be higher or lower than usual. In the case of an ectopic pregnancy, the hCG may be lower than usual and, if a woman miscarries, the level of hCG will fall quickly. If a woman develops trophoblastic disease, the hCG level may be higher than expected.

HCG is also produced by some germ cell tumours.

Repeat testing will help to monitor the hCG levels where necessary in these situations.

How is it used?

Qualitative (reported as positive or negative - 'yes' or 'no') hCG testing is routinely used to confirm pregnancy. Urine tests, such as those done at home, are qualitative.

Quantitative (reported as a number) hCG testing measures the actual amount of hCG present. Blood tests give a quantitative result and may be used to help confirm that a woman is pregnant, but are particularly useful when something is going wrong with the pregnancy, such as in an ectopic pregnancy or in a threatened miscarriage.

In addition, a quantitative hCG test may be used to diagnose trophoblastic disease or germ cell tumours of the testes or ovary. It may also be used at regular intervals to monitor the effectiveness of treatment for these conditions and to detect tumour recurrence.

When is it requested?

To tell if a woman is pregnant, a blood test can be done that may detect hCG as early as 7 days after conception. A urine test may be able to detect hCG at around the time of the first missed menstrual period.

If something is going wrong with the pregnancy, the doctor may order hCG blood tests every so often to monitor the condition.

A doctor will also request an hCG blood test if he or she suspects trophoblastic disease or a germ cell tumour.

What does the result mean?

In non-pregnant women, hCG levels in the blood are normally very low or undetectable. During early pregnancy, the hCG level in the blood doubles about every two to three days. If something is going wrong with the pregnancy, the hCG does not rise as expected and may even fall. If a woman has a miscarriage, the hCG level in the blood falls rapidly. If it does not, it may indicate remaining hCG-producing tissue that will need to be removed.

hCG is also used to monitor treatment in patients with trophoblastic disease and to detect recurrent disease after treatment is complete. During therapy, a falling hCG level generally indicates that a tumour is responding to treatment, while rising levels may indicate that a tumour is not responding to therapy. Increased hCG levels after treatment may indicate a recurrence of disease.

Is there anything else I should know?

There are a number of forms of hCG and one type of hCG is also tested as part of the screening tests done on pregnant women done to check for the risk of certain conditions in the unborn baby such as Down syndrome. This is not the same as the hCG test described in this article.