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A home pregnancy test is very accurate when the instructions are followed properly. False positives are very rare, but false negatives are more common. The most common causes of a false negative pregnancy test are testing too early, failing to follow the directions, and reading the results after the allotted time has expired.
In order to understand how a negative pregnancy test can occur, it’s important to understand how pregnancy tests work. A home pregnancy test involves urinating onto an absorbent strip. This strip will change color to indicate the presence of human chorionic gonadotropin (hCG), a hormone that is found only in pregnant women.
One of the most common causes of a false negative pregnancy test is testing too early. The hCG detected by pregnancy tests isn’t produced until the fertilized egg becomes implanted in the uterine wall, which can take up to two weeks after conception. Most women won’t produce enough hCG to register on a pregnancy test until around the time their period is due.
An early pregnancy test can sometimes detect pregnancy before a missed period, but the most accurate results come from testing a few days after a missed period. Levels of hCG typically double every two days during pregnancy, so repeating the test just a few days later can result in a positive result. When testing early, women are advised to use the first urine of the morning because it tends to be the most concentrated and thus contain the highest levels of hCG
A negative pregnancy test can also be triggered by a poor testing technique. Most home pregnancy tests need a certain amount of urine in order to make an assessment. Holding the test in an improper position while urinating sometimes results in an insufficient amount of urine soaking the test strip. Some women find it helpful to first urinate into a cup and then soak the test strip into the cup to ensure proper saturation.
Another possible cause of a negative pregnancy test result despite actually being pregnant is waiting too long to read the results. It is important to follow the instructions provided with the home pregnancy test very carefully. Many tests must be read within ten minutes before the results become invalid. A positive line on a test can fade quickly, which makes it look like a negative result.
Any time there is a doubt about the accuracy of a negative pregnancy test, further testing is recommended. Using a test from a different brand and comparing the results can shed light on the situation. Another way to eliminate doubt is to wait a few days for more hCG to build up and then repeat the test. A blood test in a doctor’s office can pick up lower levels of hCG and yield more conclusive results.