A pregnancy test measures a hormone called human chorionic gonadotropin (HCG). HCG is a hormone produced during pregnancy. It appears in the blood and urine of pregnant women as early as 10 days after conception.
A pregnancy test may be performed using blood or urine. There are two types of blood pregnancy tests:
The blood test is done 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 HCG test is usually performed by placing a drop of urine on a prepared chemical strip. It generally takes 1 to 2 minutes for a result.
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.
This test may be done to:
HCG levels rise rapidly during the first trimester of pregnancy and then slightly decline.
HCG levels should almost double every 48 hours in the beginning of a pregnancy. 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 a molar pregnancy or 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.
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.
If you think you are pregnant, repeat the pregnancy test at home or at your health care provider's office.
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Morrison LJ. General approach to the pregnant patient. In: Marx JA, Hockberger RS, Walls RM, et al, eds. Rosen’s Emergency Medicine: Concepts and Clinical Practice. 7th ed. Philadelphia, Pa: Mosby Elsevier; 2009:chap 175.