A pregnancy test measures a hormone called human chorionic gonadotropin (HCG) to determine whether a woman is pregnant. The test can be performed on blood (serum) or urine.

There are two types of pregnancy tests -- qualitative, which measures whether the HCG hormone is present; and, quantitative, which measures how much of the hormone is present.

See also:

• HCG - urine
• HCG - serum - qualitative
• HCG - serum - quantitative

The urine HCG test is usually performed by placing a drop of urine on a prepared chemical strip. It generally takes one or two minutes for the strip to indicate the result.

The serum tests are performed by drawing a single tube of blood and sending it to a laboratory. You may wait anywhere from a few hours to more than a day to get the results.

The urine test involves normal urination into a cup. The serum tests involve drawing blood through a needle and into a tube. Any discomfort you might feel from the blood draw will only last a few seconds.

Women who are late for their menstrual period (menses) often perform qualitative urine tests at home. Qualitative tests only indicate whether you are pregnant or not -- yes or no. Home pregnancy tests are available at pharmacies and do not require prescriptions.

Sometimes a qualitative test will be performed at your doctor's to confirm the results of your home test. Doctors also perform a pregnancy test before performing a procedure or prescribing a medication that might adversely affect an existing pregnancy.

The urine test can detect HCG levels above 25-50 milli-international units per milliliter (mIU/mL). Serum tests can detect HCG levels above 5-10 mIU/mL.

QUANTITATIVE TESTS

Quantitative serum pregnancy testing is usually performed at a hospital or doctor's office. This test measures the amount of HCG in your blood. It can measure amounts ranging from 5 mIU/mL to 2,000,000 mIU/mL or more.

Quantitative testing is performed when it is not sufficient merely to know whether you are pregnant or not. For example, sometimes, your doctor will need to correlate your HCG levels with the progress of your pregnancy.

Ask your doctor to explain the results of your quantitative pregnancy test.

In women who are not pregnant, both the urine and serum HCG tests will be negative. This means that the amount of HCG present in your system is less than 5 mIU/mL and, therefore, will not be detected by either exam.

In a normal pregnancy, the HCG level should rise through the entire first trimester and then fall thereafter.

HCG levels that do not rise appropriately may indicate a problem with your pregnancy. Some problems associated with an abnormally rising HCG level include miscarriage and ectopic (tubal) pregnancy.

Extremely high levels of HCG may suggest more than one fetus -- for example, twins.

Your health care provider will understand the significance of your HCG levels, and he or she should discuss the levels with you.

Possible risks from any blood test include:

• excessive bleeding
• fainting or feeling lightheaded
• hematoma (blood accumulating under the skin)
• infection (a slight risk any time the skin is broken)
• multiple punctures to locate veinsThere are no medical risks associated with testing for pregnancy.

Urine pregnancy tests will only be positive when you have sufficient HCG in your blood. If you are very early in your pregnancy, and the HCG level is below 25-50 mIU/mL, the test will be negative.

Therefore, if you are late for your period, you should wait 7 to 10 days before trying the home pregnancy test. If the test is negative, wait a few more days. If you still don't menstruate, try the test again. If you still test negative and your periods do not return to normal, see your health care provider.