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Just a few years back, home pregnancy testing was expensive and a bit more complicated than it is now - with tests offering a fraction of the sensitivity that today's diagnostic kits boast. The good news is that pregnancy testing is easy, affordable, and accurate - with early-detection tests capable of determining pregnancy as early as 8-10 days dpo.

How do Pregnancy Tests Work?
hCG and the Detection of Pregnancy

HCG pregnancy tests determine pregnancy through the detection of the hormone hCG (Human Chorionic Gonadotropin) in a woman's urine. In technical terms, hCG is a glycoprotein hormone secreted by the developing placenta shortly after a fertilized egg has implanted in the uterine lining. The appearance of hCG soon after conception - and its subsequent rise in concentration during early gestational growth - make it an excellent marker for the early detection of pregnancy.

Pregnancy tests come in two common formats - tests strips and midstream tests. To use a pregnancy test strip, you fill a clean, dry container with urine and hold the test strip in the container for several seconds. With midstream tests, you simply hold the test in your stream of urine (or you can dip the absorbent end into a container of urine). Both test formats are equally reliable - but always read pregnancy test kit instructions carefully. Though they all function by the same principle, unique manufacturing specifications and instructions may apply.

Also, the way results appear among products may differ: some brands have tests lines (horizontal lines) and other tests may indicate a "plus" sign. Newer digital pregnancy test kits will even tell you, in words, if the result is positive or negative. Indeed, things have changed quite a bit, even in the last 10 years or so!

With most home pregnancy testing products, the "reaction time" of the test is five minutes. Generally, at three to five minutes, you can interpret the test results. In some cases, a positive result will show up quickly if the hCG level is high in the urine. However, most tests require a minimum five minute interval to verify a negative result for pregnancy. Manufacturers also recommend that you should not read tests after a designated time period, as most test brands have the possibility of developing evaporation lines. If you leave the test to sit for too long, an evaporation line may develop and look like a positive result.

How do I Interpret Pregnancy Test Results?

Once the reaction time of the test is complete, color bands will appear (or fail to appear) in the test region of the strip or midstream unit. All tests have a "control" color band (or color line) that indicates whether the test is working or not. The "test" color band indicates a positive or negative result (please refer to the graphic below). Given proper testing and interpretation procedure, a faint line in the test region may be read as a positive result, though it's a good idea to verify any result with an additional test 24-48 hours later (using first morning urine).

How Early Can I Test? And When Should I Test?
Early Pregnancy Test Sensitivity

HCG is measured in thousandths of International Units, or mIU. The most sensitive pregnancy tests can detect hCG levels at as low as 20 mIU. This level of hCG is present in the urine of pregnant women at about 8 days after conception - (though conception/implantation can actually take place several days after the last recorded intercourse). Test sensitivity equates with early-detection - and the lower the number, the sooner a test can detect pregnancy.

If pregnant, the amount of hCG in your system should be around 25 mIU at 10 dpo (days past ovulation), 50 mIU at 12 dpo, 100 mIU at around two weeks dpo. Blood tests can determine pregnancy as low as between 5 to 10 mIU/hCG, though with levels of 5 mIU, a conclusive determination cannot be made without risking a "false positive" as low levels hCG can be present in the body without pregnancy.

Drugstore pregnancy tests generally detect pregnancy at 50 mIU - 100 mIU hCG, though you can find early-detection pregnancy tests on the Internet with sensitivity levels as low as 20 mIU. With all diagnostic products, take care to follow the instructions.

For earliest detection of pregnancy, use first morning urine, as this urine sample contains the most concentrated amount of hCG. If using first morning urine is not feasible, avoiding urination for several hours before using a pregnancy test.

Besides pregnancy, elevated concentrations of hCG may be found in women with trophoblastic diseases. These conditions should be ruled out in the interpretation of hCG levels to establish a diagnosis of pregnancy.

Read More About Pregnancy Tests

> Pregnancy Test FAQ: Questions about Pregnancy Testing
> Optimize: Tips for Pregnancy and Ovulation Testing
> Test Sensitivity and Early Detection
> How Early Can I Begin Testing, Faint Lines and Evaporation Lines

Test Instructions are specific to Early-Pregnancy-Tests.com products. They are re-published here as a single example of ovulation test instructions. These instructions should not be generalized to other brands.

• Pregnancy Test Instructions

> Pregnancy Test Strips
> Pregnancy Midstream Tests