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 and is not otherwise produced by women except in very rare cases of cancer. hCG builds up rapidly in your body shortly after the embryo attaches to the uterine lining following the first few days of implantation. It can be detected by a home pregnancy test three to five days after a 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 testing stick and wait 3-5 minutes for the results to appear.

How Accurate Are Home Pregnancy Tests?

Urine-based home pregnancy tests have a high rate of accuracy, 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 or womb.

Conversely, a negative result does not necessarily mean that there is no pregnancy. Since the sensitivity levels of home pregnancy tests differ, 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 healthcare provider immediately 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 healthcare provider using blood samples can detect a pregnancy one to two days after implantation. Blood tests are highly sensitive to 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: June 29, 2001
Reviewed By: Peter Chen, M.D., Obstetrics and Gynecology, University of Pennsylvania School of Medicine. Review provided by VeriMed Healthcare Network.

A.D.A.M.'s health encyclopedia is accredited by URAC, also known as the American Accreditation Healthcare Commission (www.urac.org). URAC's accreditation program is the first of its kind, requiring compliance with 53 standards of quality and accountability, verified by independent audit. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial reviewers. A.D.A.M. is also a founding member of Hi-Ethics (www.hiethics.com) and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 2002 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.