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:
Qualitative, which measures whether the HCG hormone is present
Quantitative, which measures how much HCG is present
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.
How the test will feel
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.
Why the test is performed
This test may be done to:
Determine if you are pregnant
Diagnose abnormal conditions that can raise HCG levels
Watch the development of the pregnancy during the first 3 months (quantitative test only)
HCG levels rise rapidly during the first trimester of pregnancy and then slightly decline.
What abnormal results mean
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.
Webster RA. Reproductive function and pregnancy. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 25.
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.
Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; and Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Redmond, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.