How Accurate Were Early Pregnancy Tests?

By Genevieve Hawkins

Most home pregnancy tests claim that they are 99 percent accurate, but many women have seen or heard of inaccurate results. Home pregnancy tests are tested in a lab under optimal conditions. Assume that the true accuracy of early pregnancy tests is less than what is claimed on the packaging, especially if they are used to detect pregnancy hormones on or before the first day of your missed period.


Most home pregnancy tests work by detecting a hormone called Human Chorionic Gonadotropin or hCG that builds up in the body following implantation of a fertilized egg six to eight days following conception. A blood test administered by a doctor can read levels of hCG as early as six days following ovulation. Home pregnancy tests can read the level of hCG starting around 14 days after conception. The levels of the hormone increase through the first eight weeks of pregnancy.


Almost all home pregnancy tests work by detecting hCG in your urine. Some will display two lines for a positive result and one line for a negative result, while e.p.t. shows a + sign if you are pregnant. You either place the test stick in your urine stream or you collect a clean sample in a cup, depending on manufactrurer instructions. After you have collected the sample lie the test flat with the test window facing upwards. Wait a few minutes to read the results but disregard the test after 20 minutes.

False Positive

When a pregnancy test shows a positive result, but you aren't actually pregnant, it can be the result of a recent spike in the hCG pregnancy hormone. This can happen if you gave birth, aborted or miscarried within the past nine weeks. According to a false positive can be the sign of a chemical pregnancy in which a fertilized egg is present that will be shed during your period, as happens in around 50 percent of early pregnancies. Certain prescription drugs for Parkinson's disease and convulsions or that are given as diuretics can also cause false positive results. In rare cases a false positive pregnancy test may also be a sign of tumors or ovarian cysts.

False Negative

A negative test result, when you are actually pregnant, is more common than a false positive in the early stages of pregnancy. Levels of the pregnancy hormone hCG only become readable on a home pregnancy test after your missed period. According to, taking a test on the first day of your missed period reduces accuracy to as low as 80 percent; wait a few days extra before taking a pregnancy test. Take the test right after you wake up in the morning, as your urine in the morning is more concentrated.

Human Error

Mistakes you make can lead to false readings on pregnancy tests. You may miscalculate when your period is due to start, leading you to test too early and get a false negative test result. If you are asked to collect urine in a cup be sure there is no detergent residue on the inside, as some detergents can lead to a false positive pregnancy reading. Make sure to read the test result during the time frame given by the manufacturer (usually two to 20 minutes after you place the sample). Reading the result too early may mean that the test hasn't shown the pregnancy yet. Reading the test too late may mean a thin second line has appeared that shouldn't be there.

Manufacturer Error

Sometimes you will get a test result that is neither negative or positive. This invalid reading can be caused by manufacture defect, human error or an expired test. Pregnancy tests that have expired may also be inaccurate.

About the Author

Genevieve Hawkins has been a freelance writer and editor for seven years. She graduated from Bowling Green State University with a bachelor's degree in psychology and studied for her master's degree in social psychology. Hawkins has published articles on both the Internet and in print for Valley Scene Magazine, Infosearch Media, Examiner and Investrend, and she edits corporate transcripts for Factset Research.