What does a negative pregnancy test mean – and could it be a false negative?

Home pregnancy tests are miraculous little tools: They deliver fast results, are pretty simple to use, and can cost as little as a dollar. But they're not without their quirks – including the possibility of a false negative pregnancy test.

As with any product, user error can happen. Plus, the human body is a fickle thing, and certain things can trigger a home test to say you're not pregnant when you actually are. Read on to learn more about what can cause a false negative pregnancy test and what to do if you suspect your results aren't accurate.

How accurate are pregnancy tests?

Getting a reliable reading largely depends on when and how you use the test. It all starts with peeing on a stick or into a cup – and though this is simple enough, there are common pregnancy test mistakes to avoid.

To give a little background: Home pregnancy tests are designed to check your urine for a hormone called human Chorionic Gonadotropin (hCG). The cells that will later form your placenta start to produce hCG around 10 days after conception. As your placenta develops, your hCG levels steadily tick upward, doubling every two to three days in early pregnancy. Once your system is flooded with the hormone, it's detectable in your blood and urine – and, voila, you get a positive test result.

Most pregnancy tests claim to be 99% accurate, but some are more sensitive to very low levels of hCG than others. That means you may or may not get an accurate result when testing before your missed period.

According to the Food and Drug AdministrationOpens a new window, "the different tests for sale vary in their abilities to detect low levels of hCG. There are some tests for sale that are sensitive enough to show you are pregnant before you miss your period."

Still, for the most reliable results, many experts recommend waiting to test until you miss a period or a few days after that.

In fact, the FDA says up to 20% of pregnant women won't detect their pregnancy on the first day of their missed period – because of an irregular menstrual cycle or other timing issues.

What's a false negative pregnancy test?

A false negative pregnancy test means you are pregnant but get a negative result.

Researchers at the Washington University School of Medicine in St. LouisOpens a new window estimate false negatives have appeared in up to 5% of home pregnancy tests in the past decade or so. (More on why this can happen below.)

One thing is certain: Getting an unclear or inaccurate outcome on a pregnancy test can mess with your emotions. There's a lot riding on those results.

"People can experience different emotions with a false negative test," says Layan Alrahmani, M.D., a board-certified ob-gyn and maternal-fetal medicine specialist and member of the BabyCenter Medical Advisory Board.

"For someone actively trying to conceive, a false negative can bring a wave of frustration, disappointment, and even sadness, as it might seem like another setback in an already emotional journey. Conversely, for someone who isn't planning to become pregnant, it might cause anxiety."

If you think you're pregnant and getting a false negative, wait a few days after testing and try again. If you still don't believe the results, talk to your healthcare provider, who can do a blood test or an ultrasound to determine whether or not you're expecting.

For someone actively trying to conceive, a false negative can bring a wave of frustration, disappointment, and even sadness, as it might seem like another setback in an already emotional journey.

- Layan Alrahmani, M.D., board-certified ob-gyn and maternal-fetal medicine specialist 

What can cause a negative pregnancy test?

A negative pregnancy test means the test didn't detect the pregnancy hormone hCG in your urine. The simplest explanation? You're not pregnant.

That said, certain factors can trigger a false negative pregnancy test:

• You tested too soon. Some home pregnancy tests can detect hCG the first day you miss your period (or even before then), but the earlier you test, the higher your chances of getting a false negative.
• Your hormone levels were too low or diluted. For the most accurate result, take the test right after you wake up in the morning. That's when your urine – and any hCG in it – is the most concentrated.
• You conceived later than you think. Don't time the test based on when you assume you got pregnant. Sperm can live in the fallopian tubes for up to five days, so it's possible you conceived several days after having sex. Or you might have ovulated later than you think.
• You didn't use the test correctly. Read the product's packaging and instructions carefully. Make sure you didn't check the results too soon (or too late, which can lead to an often-confusing evaporation line when the urine dries).
• The test expired or wasn't stored properly. Check the product's label for the expiration date (after this time, they can be less sensitive) and how to store it. As just one example, ClearBlue advises keeping its tests in an area with a temperature between 36 and 86 degrees.
• The test itself failed. This isn't common, but it's worth being aware of. The researchers noted above from the Washington University School of Medicine in St. Louis found that a degraded form of the pregnancy hormone, called hCG core fragment, can also be found in urine. Some tests can accidentally pick up on this fragment instead of the intact form of hCG. The research suggests that some home tests have failed to respond to the fragment, leading to a false negative even if the intact hormone is present.

Can twins cause a false negative pregnancy test?

Yes, but it's a rare phenomenon. If you're pregnant with twins or multiples, you'll have more hCG circulating throughout your system – we're talkin' a lot more.

You'd think that having plenty of hCG would lead to a positive reading, but extremely high levels of the hormone can occasionally make a home pregnancy test go haywire. So while it's very unlikely, it is possible that twins could cause a false negative. This is known as the "hook effect."

What if I have a positive pregnancy test and then test negative?

You could have had a false positive pregnancy test, meaning your test result says you're pregnant when you're actually not. While this is rare, it can happen if you've experienced a pregnancy loss, or if you took a pregnancy test too soon after taking a fertility drug that contains hCG.

It's also possible that you are pregnant, and your second test was a false negative. If your home pregnancy test is positive, or you've gotten mixed results, make an appointment with your provider to confirm what's going on.

My period is late, but my pregnancy tests are negative. Could I still be pregnant?

If you keep getting a negative result on home pregnancy tests for more than a week after missing your period, it's very unlikely that you're pregnant. (Again, you can check with your provider to be on the safe side!)

Your ovaries typically release one egg every month, and if it's not fertilized, menstruation starts about 14 to 16 days after ovulation.

If you miss more than three periods in a row and your pregnancy tests are all negative, see your doctor for a thorough evaluation. Women can stop having regular periods for a lot of reasons, including diabetes, an eating disorder, excessive exercise, being overweight or underweight, chronic physical or mental stress, and taking certain medications.

Other conditions that can affect your period include:

• Thyroid disorder: An underactive or overactive thyroid can lead to missed periods. Symptoms of an underactive thyroid (hypothyroidism) include fatigue, weight gain, and a slowed heart rate, among others. An overactive thyroid (hyperthyroidism) can cause nervousness, irritability, problems sleeping, a fast or irregular heartbeat, and weight loss. Your provider can order a blood test to determine how well your thyroid is working, and thyroid conditions can usually be managed with medication.
• Too much prolactin: You might miss a period (or more than one) if you're producing an abnormally high level of the hormone prolactin. Your body usually makes prolactin when you're nursing, which is why exclusive breastfeeding can delay periods.
• Polycystic ovary syndrome (PCOS): This condition affects the hormones that release mature eggs. If you have PCOS, your eggs remain in your ovaries, where they can't be fertilized. A telltale symptom is weirdness in your cycle, such as irregular periods and heavy menstrual bleeding.
• Perimenopause: As you approach menopause (a stage known as perimenopause), your periods become more erratic. You might also start dealing with hot flashes, trouble sleeping, mood changes like irritability, and other symptoms adjacent to full-blown menopause. This typically starts during your 40s, but some women experience perimenopause in their mid-30s.

Why am I having pregnancy symptoms but negative pregnancy tests?

You could be pregnant and dealing with a string of false negative pregnancy tests, but what if you've already ruled that out?

Other likely explanations: You might be on the cusp of your period and dealing with PMS. Or you could be ovulating. Both trigger symptoms that can make you feel pregnantOpens a new window, such as breast tenderness, cramps and abdominal pain, bloating, heavy fatigue, changes in your vaginal discharge, and mood swings.

Tell your provider about what you're experiencing, including any changes in your period. They can do a deep dive to figure out what's going on, so you can start feeling better – and know what to expect.