How Do Home Pregnancy Tests Work?

All pregnancy tests, regardless of whether they are taken at home or at a doctor's office, detect the level of human chorionic gonadotropin (hCG) in either urine or blood samples. hCG is a hormone created by the developing placenta. hCG builds up rapidly in your body shortly after the embryo attaches to the uterus. It can be detected by a home pregnancy test three to five days after a missed period. Newer and more sensitive tests can even detect the hormone several days before your missed period.

How Do I Take A Home Pregnancy Test?
Be sure to read the directions included with the pregnancy test very carefully. There are various ways the urine sample is collected and placed on the testing application. Most commonly, you will urinate directly onto a testing stick and wait 3-5 minutes for the results to appear.

How Accurate Are Home Pregnancy Tests?Urine-based home pregnancy tests are very accurate, as positive results are almost always associated with pregnancy. False-positives are rare (this is when the test shows that you're pregnant but you're not). A positive result does not guarantee that the pregnancy will succeed or is located within the uterus.

Conversely, a negative result does not necessarily mean that there is no pregnancy. Since some tests detect a lower level of hormone than others, the type you choose may not detect a pregnancy in its early stages. If you suspect you are pregnant but your test comes back negative, wait a few days and take another test.

When a pregnancy test shows a positive result, you should contact your doctor or health care provider to schedule a prenatal evaluation and exam.

How Do Blood Tests Administered By A Doctor's Office Differ From Home Pregnancy Tests?
Pregnancy tests performed by a health care provider using blood samples can detect a pregnancy one to two days after implantation -- a few days before a missed period. Blood tests can pick up very low levels of hCG and will, therefore, show results almost immediately.

All pregnancy tests are fundamentally the same — they measure the amount of hCG in your system and produce positive or negative results based on that measurement.

Review Date: 12/1/2010
Reviewed By: Zev Williams MD, PhD, FACOG, Reproductive Medicine and Infertility, Weill-Cornell Medical Center, New York, NY. Review provided by VeriMed Healthcare Network.

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