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Am I pregnant? How to read positive and negative pregnancy tests

Maybe you missed a period, or have been trying to conceive for a while – either way, here’s what you need to know about what those little blue lines mean.

Though there are a variety of pregnancy test brands on the market, they all look for the presence or absence of hCG, or human Chronionic Gonadotropic. This is a hormone made by the placenta that shows up in your blood or urine. hCG is only produced during pregnancy, which means that a positive test is a strong indicator that – yes! – you are pregnant.

Urine pregnancy tests

Urine pregnancy tests are helpful in detecting the presence or absence of hCG, not how much is floating around in your system. Because of this, you may read a false-negative result due to lower-than-normal hormone levels, or if you don’t follow the pregnancy test instructions correctly. This is why it’s always good to double-check your test results by waiting a week to re-take it or visiting your doctor for a blood-pregnancy test, which is more sensitive to hCG levels. Here’s how to get the most accurate results from a urine pregnancy test at home:

  • Read the instructions before taking the test – you don’t want to miss that small window of time when test results are most accurate by poring over the fine print.
  • Test first thing in the morning, when your hCG levels are at their highest. If that time has passed and you can’t wait, hold off from bathroom breaks for a couple of hours and take the test then.
  • Drinking to make yourself pee may seem like a good idea, but drinking too many fluids may dilute your urine and lower your hormone levels, increasing your chance for a false-negative.
  • Remember that, if pregnant, the earliest day hCG is released is about 6 days after conception. Most experts recommend taking a pregnancy test after you’ve missed a period. Because hCG levels double about every other day in a pregnant woman, the test is even more reliable about two weeks after conception.
  • If you’re taking fertility drugs, call your doctor before taking the test to ensure that your medications won’t affect the results.

It’s important to keep in mind that about half of all embryos that attach to the uterine wall will detach again, so you may read a positive result for a pregnancy that won’t progress.

False positive/false negative pregnancy tests

There is a small margin of error when it comes to home pregnancy tests that use urine to test for the presence of hCG. False results are possible when:

  • You have a growth, such as an ovarian tumor, that produces hCG
  • You’ve taken certain medications, such as infertility treatments, that contain hCG
  • hCG remains in your system after a recent birth or miscarriage
  • The test was taken prematurely – most health professionals suggest waiting a few days into a missed period to ensure accuracy. If you’ve been trying to get pregnant for some time, the extra days may seem like an eternity to wait. However, if the test is taken too early after ovulation, the test may falsely show up as negative.
  • The test kit is faulty. Make sure that your test hasn’t expired, and that you’re reading the test during the suggested window of time as listed in the instructions. Heat and moisture may also alter test results.

Blood pregnancy tests

These tests are performed in your doctor’s office, and use samples of drawn blood to measure the amount of hCG in your bloodstream. These tests can be performed as early as 8 to 10 days after ovulation. The results, unlike urine pregnancy tests, can reveal whether or not you’re pregnant as well as the amount of hCG in your blood, which is used to estimate how far your pregnancy has progressed.

These procedures are 99% accurate and can detect a much lower amount of hCG in the bloodstream than urine pregnancy tests.

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