How do Pregnancy Tests Work?

Pregnancy tests identify a special hormone in the blood or urine produced during pregnancy. This hormone is called human chorionic gonadotropin (HCG), often referred to as the pregnancy hormone. There are two basic types of pregnancy tests, blood and urine.

Home pregnancy test are primarily urine tests. These are easy to use, private and inexpensive. Most are quick and very accurate, claiming a 99% accuracy rate. Tests can be purchased at drug and discount stores without a prescription. False positives are very rare, but a false negative is possible if the test is done too early for sufficient quantities of HCG in your urine. False negatives can be avoided by waiting until your period is due, or about 2 weeks after you ovulate. Confirming a negative result with a second test a few days or a week later is wise. Always follow a positive result with a trip to your doctor for confirmation and prenatal care.

Medicines containing HCG can cause a false positive on your home test, but most over-the-counter and prescription drugs will not affect test results.

Blood test results may take a few hours or a day, and usually require a trip to the doctor or lab. There are two types of blood tests for pregnancy. The first, a qualitative HCG blood test, provides simple positive or negative results, similar to a urine test. This test is slightly less accurate than the quantitative blood test (or beta HCG test) which measures the exact amount of HCG in the blood. The beta test's ability to pick up small traces of HCG in the blood increase its accuracy.

Whichever type of test you choose, it is important to remember that a follow-up trip to the doctor is important for you and your new baby.

Maria writes for Pregnancy Due Date, a site that tries to information for expectant mothers. For more great pregnancy articles, visit our Pregnancy articles archive.