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Before You Take a Pregnancy Test

How They Work and When's The Best Time to Take One

By

Updated June 06, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Pregnancy test
Daniel Allan/Photographer's Choice RF/Getty Images
Woman holding pregnancy test

Those frequent pregnancy tests are more likely to cause anxiety than give you the early positive you're looking for.

Ray-Kachatorian / Getty Images

For many women, deciding when to take a pregnancy test is one more additional source of anxiety as the two-week wait ends. There is the part of you that is dying to know if this month will be the month you finally get pregnant, and you may feel tempted to take the test before your period is late. If you have early pregnancy signs, you may feel even more tempted.

(Wondering if you're having pregnancy symptoms? Take this fun pregnancy signs quiz.)

On the other hand, you are most likely aware that taking the test early may come up negative, even if you are pregnant. So what should you do? How do you decide when to resist and be patient, and when to pee on a stick?

Understand How Pregnancy Tests Work

Before you decide when to take a pregnancy test, it helps to understand how they work. The tests detect pregnancy hormone, human chorionic gonadotropin (hCG), in your urine. Some tests also detect a variation of this hormone, known as hyperglycosylated hCG (H-hCG). The regular hCG is produced only after an embryo implants in to the endometrium, while H-hCG begins to be released earlier, some time after fertilization.

    Levels of Pregnancy Hormones and Pregnancy Tests

    When pregnancy tests tell you how much hormone they detect, they usually tell you how much hCG the test requires. A woman’s level of H-hCG, though, is typically higher than hCG. The majority of pregnancy tests are not sensitive to the hormone H-hCG.

    If a pregnancy test does detect H-hCG, you’re more likely to get a positive result early. If a pregnancy test is not sensitive to H-hCG, and only detects regular hCG, getting an early positive result is less likely. The great majority of pregnancy tests on the market, unfortunately, are not great at detecting H-hCG.

      Understanding How Early Result Pregnancy Tests Work

      What about early results tests, though, the ones that promise results three or four days before your missed period?

      It’s important to know that these tests assume a 14-day luteal phase. (That’s the time between ovulation and when you get your period.) If your luteal phase is usually 12 days, four days before your missed period would be 9 days after ovulation. Way too early to test.

      If you have a luteal phase of 15 days, though, 4 days before your missed period is 12 days after ovulation. You still may not have enough hormone that early, but you’ve got a much better chance than someone with a shorter luteal phase.

        But What About the 99% Accuracy?

        If you read the instructions carefully, they are promising 99% accuracy on the day of your missed period — and not for early results. If you expect your period on Wednesday, Thursday would be the day of your missed period. These promises of 99% accuracy, however, may not be true! In research studies, where they compared how much hCG the test claimed to detect and how much it actually detected, the tests were only 46% to 89% accurate. In one study, pregnancy tests, on average, indicated a positive result only 80% of the time on day 28 of the woman’s menstrual cycle.

          Are You Sure Your Period is Late?

          Something else to consider is whether you know if your period is even late.

          If you chart your basal body temperature and you know how long your average luteal phase is and you see that you’re two days past your longest luteal phase, then you can be pretty darn sure your period is late.

          If you don’t chart your cycles, though, how can you know if your period is late? What if your cycles are irregular? According to the FDA’s website, out of every 100 women, 10 to 20 will not get a positive pregnancy test result on the day they think is just after their missed period, even if they are pregnant.

            Pros and Cons of Taking a Pregnancy Test Early

            So you’ve read all of this, but you still feel tempted to take a pregnancy test early.

            Consider the pros and cons:

            Pros:

            • Very small chance of getting a positive result, relieving some two-week wait stress.

            Cons:

            • Good chance of getting a false-negative.
            • Feelings of disappointment if you get a negative result.
            • Loss of cash. (Tests cost $1 to $18 per test.)
            • If positive, possibility of detecting an early miscarriage you may have missed if you hadn’t tested early.

              The Best Time to Take a Pregnancy Test

              If you want to avoid false negatives, or “false positives” (very early miscarriages), the best time to take a pregnancy test is after your period’s late. If your cycles are irregular or you don’t chart your cycles, I wouldn’t take a test until you’ve past the longest menstrual cycle you usually have.

              For example, if your cycles range from 30 to 36 days, the best time to take a test would be day 37 or later.

              Also, if you’ve have had an hCG trigger shot like Ovidrel, then you should not take an early pregnancy test. An early test may detect the remains of the fertility medication.

                The Bottom Line on Taking an Early Pregnancy Test

                If you feel as if you just can’t resist, carefully consider how you’ll feel if the results are negative. If a negative test doesn’t bother you, and you have cash to spend on pregnancy tests, go ahead.

                If a negative result is going to make your heart ache or if you’d rather not waste money on extra tests, though, then wait until you’re late. I do.

                Wondering if you're pregnant? Take a pregnancy symptoms quiz!

                More on pregnancy:

                Would you like to receive trying to conceive tips and fertility information every week? Sign up for your free fertility newsletter here!

                Source:

                Stephen A. Butler, Sarah A. Khanlian, and Laurence A. Cole. “Detection of Early Pregnancy Forms of Human Chorionic Gonadotropin by Home Pregnancy Test Devices.” Clinical Chemistry. 2001; 47:2131-2136.

                   

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