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Home pregnancy tests can be highly accurate, but only if used properly

Many women of childbearing age have probably used a home pregnancy test at some point, either to confirm pregnancy or to be sure they're not pregnant. Pregnancy tests are pretty straightforward: They detect the pregnancy hormone human chorionic gonadotropin (hCG) in urine, and give either a positive result for pregnant or a negative result for not pregnant.

Simple, right? The problem is there's still a lot of confusion when it comes to reading results. It's easier, however, when you understand two things: how the menstrual cycle works and the vagaries inherent in early testing.

The menstrual cycle

We recommend The American Pregnancy Association website for a complete overview of the menstrual cycle, but the most important thing to know is that while the first part of the cycle can be any length --11 to 21 days being most common -- it ends at ovulation. From there, the time after ovulation until a period starts is always around 14 days, give or take a day or two.

When a pregnancy test advertises that you can test four days before a period starts, it's important to know when you ovulated. If it was on day 14 of your cycle, four days before your expected period is around day 24. For someone who doesn't ovulate until day 21, four days before the expected period is day 31. This difference is why many women get false negatives on pregnancy tests. They assume their body follows an average 28-day cycle when, in fact, they're testing too early.

This is also why the scientific and medical community use the term "days past ovulation," rather than "days before expected period" when discussing fertility. Home ovulation predictor kits can help pinpoint the time of ovulation, which will help determine the best time to take a pregnancy test.

Early testing

Many women are anxious to begin testing as soon as they can, but false negatives can be a problem with testing too early. Another issue, as outlined in this article by the Mayo Clinic, is so-called false positives. Many pregnancies end almost as soon as they begin, and under normal circumstances you wouldn't even know you were pregnant because your period would start close to its regular time. However, a very early miscarriage still leaves a small amount of hCG in your system, and a very sensitive pregnancy test will detect that.

Other reasons for false positives are reading the test after the recommended time -- a common practice that's strongly discouraged -- or simply not wanting to believe the results. Neither can be blamed on the test manufacturer.

Home pregnancy tests are pretty much alike

To use a home pregnancy test, you either urinate on a stick or collect urine in a clean container and dip the stick. Experts recommend testing first thing in the morning, especially early in the cycle, because concentrations of hCG in urine are at their highest. Results are read in two to five minutes, although users further along in their cycles often see positives much sooner due to their higher levels of hCG.

Earlier in the cycle, especially with non-digital pregnancy tests, the results line can be very faint; try testing a few days later if you're unsure of the result. All pregnancy tests have a control line that's activated by moisture and indicates the test is working. Digital pregnancy tests use a flashing clock or hourglass as the control symbol while manual tests use a line.

All manufactures say their home pregnancy test products can detect pregnancy 99 percent of the time on the day of a missed period. Independent studies give a good overview of how sensitive these tests really are and when they're most accurate. We carefully consider these scientific studies, as well as hundreds of reviews and statistics on pregnancy test results by thousands of women, to recommend the most accurate home pregnancy test for whenever you choose to test.

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