A false negative pregnancy test happens when your pregnancy test says you’re not pregnant — even though you are.
Some reasons for a false negative are more easily identifiable, like taking a test in early pregnancy when the hormones used to detect pregnancy aren’t very high just yet.
But did you know that a twin pregnancy can be another reason your test comes out negative?
This guide from PregnancyResource.org explains how pregnancy tests work, what causes them to show a false negative result, and how a twin pregnancy can contribute to this.
How Do Pregnancy Tests Work?
An at-home pregnancy test works by measuring levels of a specific hormone in your urine called human chorionic gonadotropin (hCG).
While everyone has hCG in small amounts, levels of hCG increase during pregnancy to help grow the uterus and prepare it for pregnancy and childbirth.
A positive pregnancy test detects a higher concentration of hCG.
Your body begins to ramp up its hCG production shortly after a fertilized egg implants itself into the uterus.
Depending on the person, this can begin 6-12 days after conception. After this happens, hCG levels double nearly every 48 hours and peak in the first trimester.
Home pregnancy tests are different in how they accomplish this. However, nearly all of them will ask you to place a drop of urine on a designated strip.
This strip contains antibodies that react with hCG and produce a change in color if higher-than-normal levels are detected.
Depending on the test that you use, you may see a second vertical line (which can show up as a very faint line!), a plus sign, or the words “pregnant” on the display.
If you are not pregnant, then you may not see any changes on the display, a negative sign, or “not pregnant.”.
If you head to your primary healthcare provider or obstetrics/gynecology provider for testing, you would likely be given a blood test to check hCG levels.
What Is a False Negative Pregnancy Test?
Sometimes, you can follow the directions on your pregnancy test kit to a T and not see any changes to the display. This often means that the test didn’t detect a larger amount of hCG in your urine and that the results are “negative.”
This can rightfully make you think that you’re not pregnant. In most cases, this will be the case.
However, it is also possible for the test to say you’re not pregnant when you actually are. This is referred to as a “false negative.”
On the other hand, if you aren’t pregnant but the test says you are, then the result is a “false positive.”
False negatives are more common than false positives. Keep reading to find out why a twin pregnancy can cause them — and if it’s not twins, what the reason for a false negative could be instead.
Can Twins Cause False Negative Pregnancy Test Results?
If you’re pregnant with twins or triplets, you will have extra-high levels of hCG.
Intuitively, this should give your pregnancy test more to work with and increase your chances of getting a positive result early in the pregnancy, right?
Well, too much hCG can actually throw off an at-home hCG test. This is referred to as the high-dose hook effect.
In simple terms, this happens when the antibodies on the test strip get “overwhelmed” with the amount of hCG that they encounter.
As a result of too much hCG, a pregnancy home test can show a false negative result.
What Else Can Cause a False Negative Pregnancy Test?
Having twins on the way is far from the only reason you may encounter a false negative result.
False negatives are fairly common and can happen due to any of the following reasons:
Testing Too Early
Getting the news that you’re pregnant can be one of the most exciting moments in your life.
Naturally, you may not want to put it off, so you take your test just several weeks after stopping birth control and trying to conceive.
But the earlier you take your pregnancy test, the less hCG there will be in your urine.
After all, it takes about 10 days after conception for there to be detectable hCG levels in your body.
If you take a pregnancy before then, it likely won’t pick up on the only slightly elevated levels of this hormone, ultimately resulting in a false negative.
It’s generally recommended to wait until after your first missed period to take a pregnancy test.
This will reduce the potential disappointment of a false negative result even with what may seem like symptoms of pregnancy such as morning nausea.
Highly-Diluted Urine
You need to drink some water before taking a pregnancy test.
But if you overdo it, the water can actually dilute the hCG molecules in your urine, making it hard for a pregnancy test to pick up on increased levels.
To help ensure your urine isn’t over-diluted, it’s best to drink as little as possible in the hour leading up to your pregnancy test.
Another trick to try is taking your test first thing in the morning — this is when your urine is at its most concentrated.
Faulty Pregnancy Test
Home pregnancy tests are regulated by the FDA, which means that they’re highly accurate (even the cheaper ones you’ll find at dollar stores and gas stations).
However, if you’re using an expired test or a test that was exposed to excessive heat, then it might not work as well and may give you a false negative result.
If you have an old pregnancy test lying around, it’s best to toss it and to head to the drugstore for a new one for the most accurate results.
In Summary
Although it’s very rare, a pregnancy with twins can “overwhelm” a home pregnancy test and cause a false negative result.
Other causes of a false negative include using an expired test, drinking too much water before the test, or taking the test too early in the pregnancy.
For the most accurate results, wait until after your first missed period to take a pregnancy test. You may already have pregnancy symptoms, but you should still wait until after your first missed period.
Avoid drinking too much water before taking the test, and buy new pregnancy tests as you need them to avoid an inaccurate result caused by expiry or poor storage conditions.
References and Sources:
Human Chorionic Gonadotropin: The Pregnancy Hormone and More | PMC
Bridget Reed is a Tampa-based content development manager, writer, and editor at GR0; specializing in content related to varying fields including medicine, health, and small businesses. Bridget went to St. Petersburg College and majored in Management and Organizational Leadership.
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