Pregnancy Tests: Frequently Asked Questions

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Q: How do home pregnancy tests detect pregnancy?

Home pregnancy tests detect the presence of the hormone hCG in a woman's urine. HCG (human chorionic gonadotropin) is a glycoprotein hormone secreted by the developing placenta shortly after fertilization.

Once the egg implants in the uterine lining, hCG is produced and secreted by the placenta. hCG can be detected in blood samples and in urine samples. Urine pregnancy tests detect hCG and will indicate a positive result when the hCG level in a sample reaches a specific threshold. If the amount of hCG in the urine sample is sufficient to exceed the threshold - or sensitivity level - a "test line" will appear indicating a positive result. If the hCG quantity in the urine sample is below this sensitivity level, no test line will appear, indicating a negative result for pregnancy.

Q: Does the hCG sensitivity of the test matter?

The sensitivity of a pregnancy test determines how soon after conception pregnancy can be detected by the diagnostic kit. Concentrations of hCG are reported in milliInternational Units (mIU) or amounts equal to 1/1000th of an IU per milliliter. Pregnancy tests with a sensitivity of 20 mIU/ml are more sensitive than tests with 50 to 100 mIU/ml.

With 20 - 25 mIU/ml tests, high sensitivity equates to early detection of pregnancy. That means you can begin testing accurately as early as eight days after conception. Conception may take place several days after date of intercourse, so the date of intercourse should not be viewed as the necessary day of conception.

Q: How accurate are home pregnancy tests?

Under laboratory conditions, home pregnancy tests are 99% percent accurate. Inaccuracies are most often traced or errors in application or failure to follow instructions with care. There are circumstances and variables - discussed in questions below - that may impact pregnancy test results (from fertility medications to dilution of urine sample). Please note that if you test too early for pregnancy, for example, just a few days after conception, then a negative result should not be regarded as conclusive. Different test kits have different sensitivity levels; therefore, read the instructions to determine when you should begin testing and ensure you follow instructions to optimize results.

Q: How long do I need to hold my urine? Is first morning urine the best sample?

Because home pregnancy tests detect hCG, it is best to collect urine samples containing the highest presence of the hCG hormone. Diluted samples (from drinking high volumes of water / frequent urination) are not recommended and can diminish test accuracy. Instead, first morning urine is considered the ideal sample as it contains the most concentrated presence of hCG. Otherwise, waiting several hours after last urinating to take a test.

Q: If the test band is faint, is the pregnancy test positive?

If the test is faint (in comparison to the control band), the test may be positive, though the presence of hCG in the woman's body - or urine sample - may be low. The presence of hCG doubles every two days in a pregnant woman. In cases where a faint test color band is present, it is recommended that you retake the test the following day using first morning urine. With most tests, a faint test band does indicate a positive result.

Q: How is it possible to receive a "False Positive" result on a pregnancy test?

False positive tests are rare - though there are instances and conditions where they can occur. For example, some tissues in a non-pregnant woman can produce hCG, though the levels are usually so low they are not detectable by home pregnancy tests (though our tests are the most sensitive on the market). Secondly, research indicates that half of all "conceptions" (fertilized eggs) do not go forward as developing pregnancy. Within this group, a proportion are recognized as "a chemical pregnancy" - a pregnancy in which there is a positive pregnancy test and no other signs or symptoms).

Moreover, a percentage of "false positive" pregnancy tests can be attributed to misinterpretation of results due to a failure to follow test instructions with precision. You should not rely on any positive result that does not show up within the time limit stated in the test instructions (see next question below).

Q: What if the test is negative after the minute reaction time, but becomes positive after an hour or more? Is this an evaporation line?

Do not attempt to interpret results after the test reaction time specified by the manufacturer. You should not rely on any positive result that does not show up within the time limit stated in the test instructions. All pregnancy test brands have the possibility of displaying an evaporation line.

Q: Can I be pregnant and not get a positive HPT (a False Negative result)?

False negative results are more common than false positives. A false negative result can stem from using a diluted urine sample and/or from taking a test too early in pregnancy. First morning urine contains the most concentrated presence of hCG - which makes it the ideal sample for pregnancy testing.

Additionally, at the same gestational stages, women produce quantitatively different levels of hCG - which means that the first indication of a positive result on a home pregnancy test may vary between women, despite similar gestational stage. If you suspect you are pregnant, you should see your doctor for a blood hCG test no matter what result you get from any home pregnancy test.

Q: Can fertility drugs or medication interfere with pregnancy test results?

The only medications that can cause a false positive on a home pregnancy test are those than contain hCG itself. If you are taking fertility medications with hCG - e.g. Novarel, Profasi, Pregnyl - please consult your doctor regarding appropriate times and circumstances for testing. Other fertility drugs and medications that do not contain hCG will not precipitate false positive results. Similarly, progesterone will not cause a false positive as well.

How do I Interpret Pregnancy Test Results?

Once the reaction time of the test is complete, color bands will appear (or fail to appear) in the test region of the strip or midstream unit. All tests have a "control" color band (or color line) that indicates whether the test is working or not. The "test" color band indicates a positive or negative result (please refer to the graphic below). Given proper testing and interpretation procedure, a faint line in the test region may be read as a positive result, though it's a good idea to verify any result with an additional test 24-48 hours later (using first morning urine).

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