Pregnant But A Negative Home Pregnancy Test
Taking a home pregnancy test can be exciting, but it also may be stressful. That's especially true if you're not sure whether you should trust the results. Know when and how to take a home pregnancy test. And learn some of the possible drawbacks of home testing.
pregnant but a negative home pregnancy test
The timing of ovulation makes a difference in the accuracy of a home pregnancy test. And ovulation can change from month to month. A fertilized egg also can implant in the uterus at different times. That can affect the timing of when HCG starts to be made and when it can be found with a home pregnancy test. Irregular menstrual cycles also can affect pregnancy test results, as they make it hard to figure out when a period should start.
For most home pregnancy tests, you put the end of the test in your urine stream, dip the test in a container of urine or put several drops of urine onto the test. A few minutes later, the result appears. It's often a plus or a minus sign, the words "yes" or "no," one line or two lines, or the words "pregnant" or "not pregnant."
Many home pregnancy tests claim to be 99% accurate. But home pregnancy tests differ in their ability to find a pregnancy in people who have recently missed a period. If you get a negative test result, but you still think you might be pregnant, take another test one week after your missed period or contact your health care provider.
Fertility medication or other medicine that contains HCG might affect home pregnancy test results. Most medicines, though, including antibiotics and birth control pills, don't affect the accuracy of home pregnancy tests.
A false-positive might happen if you had a pregnancy loss soon after the fertilized egg attached to the uterine lining. You also may get a false-positive if you take a pregnancy test soon after taking fertility medicine that contains HCG. Problems with the ovaries and menopause also might lead to a false-positive test result.
Almost everything having to do with pregnancy involves waiting: waiting until your period is due to take a pregnancy test, waiting those looooooong 3 minutes to check the results, waiting until the next month to try again, waiting 9 whole months for your baby to be born once you actually get pregnant.
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Each year, women in the U.S. rely on some 20 million home pregnancy tests to learn potentially life-altering news. Despite marketing claims that such tests are 99 percent accurate, research at Washington University School of Medicine in St. Louis over the past decade has shown that up to 5 percent of pregnancy tests return results indicating a woman is not pregnant when, in reality, she is.
Makers of pregnancy tests advise that tests taken in the first week or two after conception could be inaccurate because pregnancy hormones may not have risen high enough to be detected. But Ann Gronowski, PhD, a professor of pathology and immunology, and of obstetrics and gynecology, and medical director of core laboratory services at Barnes-Jewish Hospital, discovered that pregnancy tests can also give incorrect results to women five weeks or more into their pregnancies, when hormone levels tend to be very high. She published the first paper describing this problem in 2009, and since then has continued studying and raising the alarm on this serious but under-recognized issue. Recently, she and colleagues published a paper in the journal Clinical Chemistry, in which they evaluated how likely several pregnancy devices were to give false negative results.
But a degraded form of the hormone also can be found in the urine, and in some devices the first antibody will bind to the degraded form. The amount of the degraded form, called hCG core fragment, goes up as pregnancy progresses. The more of the fragmented hormone that is around, the more likely the first antibody will accidentally capture the fragment instead of the intact hormone. However, the signal antibody does not respond to the fragment so it does not change color when that happens, and therefore you get a negative result even though the hormone might be present.
It depends on the device. They all use different antibodies, and some are better at discriminating the full hormone from the fragment than others. We looked at 11 of the most commonly used hospital pregnancy tests to see if they were susceptible to false negatives when levels of the hormone fragment were high. Seven were somewhat susceptible, two were highly susceptible, and only two tests were not susceptible. The worst one gave false negatives in 5 percent of the urine samples of pregnant women tested. That was, unfortunately, the test we were using when that initial patient came in. Based on our research, we have switched to a test that does not have this false-negative problem.
Based on our work, the Food and Drug Administration has acknowledged the need for pregnancy tests that are not susceptible to false negatives. The FDA requires that all new tests generate a positive signal even when concentrations of the fragmented hormone are high. Unfortunately, this requirement does not apply to tests that were already FDA-approved.
Pregnancy tests work by measuring the levels of the pregnancy hormone human chorionic gonadotropin (hCG) in your urine. The amount of hCG in your body starts to increase once a fertilized egg implants in your uterus, and can be detected about 10 days after conception.
Where you are in your cycle also matters. "Most pregnancy tests will perform well if it is at the time of your missed period, which would typically be 2 weeks after ovulation or 28 days after your last period started," says Pamela Berens, MD, an OB-GYN with UT physicians and the McGovern Medical School at UTHealth in Houston.
Pregnancy tests may also be defective. However, this is more the exception than the norm since many tests come with a control indicator to prove that the pregnancy test is working properly. This indicator may show up as an additional line that appears next to the test line or a symbol that appears in a window, depending on the type of test you take.
Getting a false negative on a pregnancy test is relatively rare, but it is possible, particularly if you take a test soon after ovulation. To reduce your risk of a false negative, take the test first thing in the morning and follow test instructions carefully.
If you got a negative reading from a pregnancy test but later learned that you were pregnant, how did the test get it wrong? What causes false-negative pregnancy tests? There are a few ways that the test could read your urine wrong.
Manufacturers who market tests in both Europe and the USA tend to conform to these definitions across both markets (e.g. Clearblue, First Response, and EPT brands). Device accuracy, which is usually considered to be the percentage of correct detection of negative and positive results (at concentrations of hCG greater than test sensitivity) using urine samples from women seeking to know pregnancy status, are also often calculated. However, it is unclear as to whether other tests available in Germany conform to these definitions and it is therefore not possible to make objectivecomparisons between tests based on their packaging claims.
Unfortunately, no recent studies have investigated home pregnancy test performance, and indeed, there are no historical studies evaluating the myriad tests now available on the German market. In the absence of any available data on test performance and the lack of standardisation for evaluating test credentials, any declaration of test accuracy on the package labelling is potentially misleading.
The type of test format is another factor that can influence the accuracy of pregnancy tests when used at home. Home pregnancy tests are available in three main formats: strip, cassette and midstream test sticks. Strip tests have no casing or sample application wick; they therefore require women to collect a urine sample and then dip the small strip-like device into the sample until the urine reaches a prescribed line on the strip. The cassette format requires women to collect a urine sample, following which the user has to add a small quantity of the collected urine to thecassette-like test device using a plastic bulb supplied with the test. Both the strip and cassette test formats were primarily designed to be used by healthcare professionals in a clinical setting. However, they are also available for women to use at home. In contrast, the midstream test stick format was specifically developed to enable women to carry out pregnancy tests easily at home. Midstream test sticks consist of a stick with an absorbent wick at one end, which is placed in the urine stream or dipped into collected urine to obtain a sample.