What Can Cause a False Negative Pregnancy Test?

Published June 2nd, 2022 by Bridget Reed
Fact Checked by
Camille Freking
Medically Reviewed:
Chris Riley

Receiving an accurate pregnancy test result is important; at-home pregnancy tests are highly accurate when used as directed, but it is still possible to experience a false negative pregnancy test result. 

Excessive exercise, irregular periods due to thyroid issues or other medical conditions, ectopic pregnancy, and much more can affect the accuracy of urine pregnancy test results.

Here’s what to know about false negative pregnancy tests. 

How Do Pregnancy Tests Work?

Pregnancy tests work by detecting a certain amount of a hormone called human chorionic gonadotropin (hCG) in the urine.

Because the hCG hormone is produced in larger amounts during early pregnancy, hCG is often referred to as the pregnancy hormone. 

The body begins increasing levels of hCG immediately after conception, with the amount of hCG in a woman’s body doubling every 72 hours until peaking around weeks 8 to 12 of pregnancy.

Thus, taking a pregnancy test at the right time is important, or a false negative pregnancy test can occur.

What Can Cause a False Negative Pregnancy Test?

There are a number of different reasons why a woman might get a false negative pregnancy test result even though she is actually pregnant.

The most common reasons include taking the test well before an expected period, improper use of the pregnancy test, inaccurately timed menstrual cycle, diluted hCG levels, birth control pills or fertility drugs interfering, or overly concentrated hCG levels.

Taking the Test Too Early

The most common reason for a false negative pregnancy test is taking the test too early.

Women who are trying to get pregnant often want to test as soon as possible, and the temptation to take the test a day or two early can be overwhelming. 

However, hCG levels cannot be detected until about ten days after conception, and even then, the levels could be too low. 

At the earliest, women should wait until at least the first day of a missed period to take a pregnancy test. 

If possible, wait several days or even a week after a missed period to take the test in order to ensure that hCG levels are concentrated enough to be detectable. 

The exact timing of conception can vary depending on when a woman ovulates, so waiting until several days after a missed period is a good way of helping to make sure you get the most accurate possible result.

Improper Use of the Pregnancy Test

Pregnancy tests are generally simple to use, but it’s still important to follow the instructions.

Even if you have taken a pregnancy test before, each test is different and comes with its own directions for use.

Improper or incorrect use of a pregnancy test can yield a false negative result

Make sure to follow the directions on the package exactly. If you are confident that you are pregnant but still receive a false negative pregnancy test result, go to a healthcare provider to get tested.

They will follow recommended women’s health protocols to ensure you get an accurate result, which usually involves administering a blood test that can more accurately detect hCG hormone levels.

Also make sure to to discuss any pregnancy symptoms you’re experiencing with your obstetrician-gynecologist (OBGYN).

Inaccurately Timed Menstrual Cycle

Many women take a pregnancy test because they miss their last period.

However, not everyone’s cycle is completely regular, and even some women who normally have regular cycles can experience fluctuations from time to time. 

Using a period tracker app can help you understand the idiosyncrasies of your individual cycle, but it still may not be entirely predictable, particularly if you have certain medical conditions like polycystic ovary syndrome (PCOS) that can cause imbalanced hormones.

The average menstrual cycle is anywhere from 21 to 35 days long.

If you take a pregnancy test prior to what would be the start of your period, it’s likely that the amount of hCG in your bloodstream would be too low to be detectable by an at-home pregnancy test, possibly resulting in a false negative test.

Diluted HCG Levels

One common reason for a false negative pregnancy test result is diluted hCG levels.

In general, it is recommended that women take a pregnancy test during their first bathroom visit of the day when hCG is at its most concentrated.

Taking a pregnancy test later in the day, after recently urinating, or after drinking too much water can dilute hCG levels to the point that they are not detectable by the test, resulting in a false negative pregnancy test result. 

If it’s not possible to take a pregnancy test first thing in the morning, make sure to wait at least a few hours before going to the bathroom again in order to allow the hCG levels to become concentrated enough to be detected. 

Overly Concentrated hCG Levels

It might seem hard to believe, but it is possible to get a false negative pregnancy test result if you have too much hCG in your urine, i.e. if the hCG is too highly concentrated.

While it is rare for people to experience a false negative result due to high hCG levels, when it does happen, it occurs as a result of something called the “hook effect.” 

Pregnancy tests are calibrated to detect hCG at a specific range in the urine since most women take them during the early weeks of pregnancy.

However, hCG levels double every 72 hours at the beginning of a pregnancy, reaching their peak sometime between weeks 8 to 12. 

If your urine has too much hCG in it, the test strip may struggle to bond with the molecules of hCG, returning a negative result. 

The Bottom Line

The most common reasons for receiving a false negative pregnancy test result include taking the test too early, improper use of the pregnancy test, inaccurately timed menstrual cycle, diluted hCG levels, or overly concentrated hCG levels. 

If you are experiencing early signs of pregnancy, the best way to get an accurate result is to take a pregnancy test one or more days after a missed period and follow the instructions on the packaging carefully — don’t forget you can always schedule a visit with your women’s health provider for testing and general guidance, too.

References and Sources:

Home pregnancy tests: Can you trust the results? | Mayo Clinic 

hCG Levels | The American Pregnancy Association 

Polycystic Ovary Syndrome (PCOS) | Johns Hopkins Medicine 

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