FDA allows misleading claims on home pregnancy tests

Loopholes in U.S. Food and Drug Administration (FDA) regulations and natural variations in a woman's menstrual cycle can make the claims that appear on packaging for home pregnancy tests inaccurate or just plain false. With a claim that results are more than 99 percent accurate, one would assume a pregnancy test could detect 99 percent of pregnancies. However these claims are not based on scientific studies of a home pregnancy test's sensitivity to human chorionic gonadotropin (hCG), but rather how accurate a pregnancy test is when compared with other HPTs. A new HPT submitted to the FDA only needs to prove that its results concur with that of one already on the market 99 percent of the time to make the claim that it's more than 99 percent accurate.

In addition because HPTs work by detecting hCG, which is only produced after a fertilized egg implants in the uterus, natural variability in ovulation, implantation and hCG concentrations in the initial weeks of a pregnancy, can greatly affect a test's accuracy. Scientific studies have shown that up to 10 out of every 100 women will not have implanted by the first day of their missed period. As such, it is impossible to make a claim of more than 90 percent accuracy before or on the first day of a missed period.

Tests such as First Response Early Result that market themselves has having the ability to give results 6 days before a missed period aren't guaranteeing that they can detect all or even close to all pregnancies six days before a missed period, because it is biologically impossible to make such a guarantee. Rather these tests' high sensitivities to hCG allow to them to potentially detect a pregnancy as early as six days before a missed period. To reliably detect up to 97 percent of pregnancies with any test, a woman would have to wait until a full week after her missed period, hence the recommendation by experts to always retake a pregnancy test one week after the initial test.

In addition, scientific studies in the past 10 years have shown that the hCG present in a woman's urine during the first weeks of pregnancy is actually a mixture of many forms of hCG. More than half of the hCG present is actually hyperglycosylated hCG (H-hCG), and a test's sensitivity to regular hCG does not guarantee it will be equally sensitive to H-hCG. Still, the FDA only requires that home pregnancy tests be calibrated to regular hCG. As a result the reported sensitivity of a home pregnancy test may be very different in real life than it is under laboratory testing.

Tips for choosing a home pregnancy test

When buying a home pregnancy test, experts say to consider the following:

  • Sensitivity of the test. Most home pregnancy tests on the market today are able to detect 25 mIU/ml of human chorionic gonadotropin (hCG), which corresponds to a detection of about 90 percent of pregnancies on the first day of a missed period. The more sensitive the test the earlier you can potentially test. According to one study, though, 90 percent may be your maximum accuracy on the first day of a missed period because in 10 percent of women the fertilized egg will have yet to implant. For some women less sensitivity may actually be better (see below).
  • One-step kits are generally considered the most convenient to use. The test strip can either be held briefly in the urine stream or dipped into a collection cup.
  • Test results may be easier or more difficult to read, depending on the design. A fair degree of contrast between the line or symbol and the background is important. Digital tests can help you avoid some interpretation anxiety, but even they can have reading errors.
  • Check expiration dates. Each pregnancy test should have an expiration or best if used by date printed on the box or on the foil around the test. The chemicals used in the test can deteriorate over time and give you faulty results, so it's best to use a test that is fresh.
  • Buy more than one test. You can always use a second home pregnancy test. If your periods are irregular or you're testing before or at the time of a missed period, taking a second test a week later will increase the accuracy of your results. Most kits come with at least two tests, and buying a double package is generally a better buy than paying separately for a second kit.

Using a home pregnancy test kit

Once you buy a home pregnancy kit, here are some tips to optimize your test results:

  • Use first-morning urine. Home pregnancy tests (HPTs) detect pregnancy by the concentration of hCG in a woman's urine. First-morning urine will be the most concentrated and will therefore give you the best results. If you can't wait until morning, you can optimize the concentration by not urinating for several hours before the test and avoiding drinking large quantities of fluid, which can dilute your urine.
  • Read the instructions. Each HPT will have explicit instructions on how to use and interpret the test. Make sure to read the test after the time allotted. If you let the test sit for too long an evaporation line may develop and look enough like a positive result to cause confusion.
  • Store the tests in a cool, dry location. Exposing HPTs to extreme temperatures or direct sunlight can alter the chemicals used in the tests and make the results unreliable.
  • Know if hCG is already present in your body. All HPTs work by detecting hCG in a woman's urine, but there can be other reasons for hCG to be present in your body beside pregnancy. If you recently gave birth or miscarried, you may still have small amounts of hCG present in your body. As a result, it may be better to use a less sensitive pregnancy test to ensure your positive result is due to a new pregnancy. Some fertility drugs, such as Novarel, Profasi and Pregnyl, also contain hCG and can cause a false positive on a HPT. If you're on any of these medications it's best to consult with your doctor about when and how to test.
  • False negatives are more common than false positives. Medical experts point out that in as many as 10 percent of pregnant women, the fertilized egg doesn't implant until after the first day of a missed period. Until implantation occurs and the placenta begins developing, there is no hCG in the body to be detected by a pregnancy test, so you may test negative when you are in fact pregnant. It is always best to take a second test a week later, that way you won't be wondering if you're really not pregnant or if you just took the test too soon.
  • Other factors can affect the results. Medications such as chlorpromazine (also known as Thorazine and usually prescribed as a treatment for psychotic disorders, such as schizophrenia) and methadone (also known as Dolophine or Metadose and usually prescribed to relieve moderate to severe pain) have been reported to alter the results of home pregnancy tests as have excess blood or protein in the urine. If you have concerns, check with your doctor about your results.
  • Always follow-up with your doctor. If the results of your HPT are positive or you have questions or concerns, make sure to follow-up with your doctor. Your doctor can perform a blood test to confirm if you are pregnant and can follow the hCG quantitatively to make sure the pregnancy is progressing as expected. In addition your doctor can help you with any lifestyle or medication changes necessary for the pregnancy.

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