8 Possible Causes for a False-Positive Pregnancy Test
OTC tests are more sensitive than ever, meaning that when they pick up on pregnancy hormones in your pee, the result isn’t always a pregnancy.
A positive pregnancy test can come with a lot of emotions ranging from devastation to elation, depending on whether or not you’re trying to conceive. But what can be even more emotional (and confusing)? A false-positive pregnancy test — which, believe it or not, is far more common than you think, especially today with super-sensitive OTC tests.
So, what is a false-positive pregnancy test and why does it happen? Here, eight possible reasons, plus how to get a more accurate reading on your at-home stick.
What Is a False-Positive Pregnancy Test?
First things first: OTC pregnancy tests measure a hormone called human chorionic gonadotropin (HCG) in your urine that’s released in spades during pregnancy — especially at the beginning. As long as you are taking the test correctly (more on that later), a positive result means there is HCG in your urine, explains Jaime Knopman, M.D., director of fertility preservation for CCRM New York.
But here’s the thing: HCG can be present at low levels in the body even you're not pregnant — and just because a test is positive for HCG doesn’t mean that the pregnancy is going to progress normally. While you’ve likely heard that 10 to 20 percent of known pregnancies end in miscarriage, the true number is likely higher because miscarriages can happen before you even know you’re pregnant. “Nearly 25 to 30 percent of early positive pregnancy tests do not progress normally,” estimates Dr. Knopman. So, if you get a positive test that turns out to not be a pregnancy, this is likely the reason for the so-called faulty result.
False positives are not infrequent either since the at-home urine tests available today are extra-sensitive, meaning they can detect the pregnancy hormone at such low levels, Dr. Knopman says. “With the old tests, you needed a higher amount of HCG in the urine,” she says. In other words, years ago, a pregnancy test might not show as positive until after you miss your period, but now (as you've likely seen in many pregnancy test commercials) you can get a positive result a few days before you even miss your period.
What Causes a False-Positive Pregnancy Test
The reasons for a false-positive pregnancy test range from testing too early and picking up on a pregnancy that didn’t progress (the most common reason) to using a test incorrectly (womp, womp) and even, potentially, the effects of some medications (much more rare).
Here, a look at what might be going on if you get a positive test only to find out you’re not truly pregnant.
1. You had a chemical pregnancy.
“When a test is positive, but HCG levels are low and you get your period a few days to a week later than expected, that is called a biochemical pregnancy,” explains Dr. Knopman. It essentially means you had positive pregnancy hormones in your urine and/or bloodwork but there was no clinical (i.e. ultrasound) evidence of pregnancy, she says. Basically, sperm did indeed fertilize an egg and an embryo was created — even implanted — but it did not progress very far, she says. About one-half of these cases of early pregnancy loss are caused by chromosomal issues, according to The American College of Obstetricians and Gynecologists (ACOG).
2. You had an ectopic pregnancy.
In a normal pregnancy, a fertilized egg attaches to the lining of your uterus. But an ectopic pregnancy is when a fertilized egg gets stuck en route to your uterus and grows somewhere else, usually in a fallopian tube. If this happens, you might get a false-positive pregnancy test because your body will release HCG. The thing is, a fertilized egg can't survive outside of the uterus. If you don’t miscarry naturally — and you notice severe abdominal or pelvic pain with bleeding, extreme lightheadedness, or shoulder pain — see your doctor ASAP. Ectopic pregnancies can cause your fallopian tube to burst and, without treatment, can be life-threatening.
3. You tested too soon after a miscarriage or giving birth.
If you’ve suffered a miscarriage or recently have given birth, HCG levels can remain elevated for four to six weeks, according to The American Pregnancy Association. Test for pregnancy before this timeframe and your levels might still not be back at your pre-pregnancy range, which means you could potentially notice a positive test, which would likely be a false positive.
4. You didn’t use the test properly/the test is not working properly.
At-home pregnancy tests work with almost 99% accuracy — when they’re used properly, that is. That’s an important distinction. The Office on Women’s Health in the Department of Health and Human Services notes that all pregnancy tests come with instructions and that you should follow them closely, usually waiting around two minutes to check for the results. Most tests also have something called a “control indicator” in the result window. This tells you that the test is working properly. If the control line or symbol doesn’t appear? The test isn’t working properly so you could get a faulty result.
5. You have a molar pregnancy.
A molar pregnancy (a.k.a. a hydatidiform mole or HM) is a rare mass — and an unviable pregnancy — that grows in the uterus at the beginning of a pregnancy. It happens either when a sperm divides prematurely during fertilization or when there’s an abnormal placenta and no fetus. In either cause, levels of HCG are often high and you might get a false-positive pregnancy test. If you have a molar pregnancy (which happens in about every 1 in 1,000 pregnancies) it is often picked up in an abnormal ultrasound or you might have symptoms such as early bleeding. Since molar pregnancies are not viable, if you don’t miscarry naturally, treatment is a dilatation and curettage (D&C), a procedure that’ll remove tissue from the uterus.
6. You’re on medication with HCG in it.
Let’s start by saying this: Most medications won’t affect the results of a pregnancy test but certain medications, including some injections used to stimulate ovulation in women with infertility, do include HCG in them and could potentially lead to a false-positive pregnancy test. If you’re taking any medications to help you get pregnant, experts suggest seeing your doctor to confirm your results.
7. You’re past the point of pregnancy.
Sometimes, women who are post-menopausal or going through menopause have high levels of HCG, which could cause a pregnancy test to show as positive even though you wouldn’t truly be pregnant.
8. You have a medical condition.
This is a rare one, but some medical conditions such as certain kinds of cancer, chronic kidney disease, as well as problems with your ovaries could cause the body to have increased levels of HCG and potentially lead to a false-positive pregnancy test.
Okay, But What About a False-Negative Pregnancy Test?
Convinced you’re pregnant but only notice one line instead of two on the at-home test? Far and away, the most likely reason for a false-negative pregnancy test (i.e. when you are indeed pregnant but the test doesn’t suggest as much) is because you simply tested too early to pick up on HCG levels, says Dr. Knopman.
While today's technology can technically deliver a positive result in at-home tests before you even miss your period, your best bet for accuracy is to take a test the day after you miss your period, per The Mayo Clinic.
Get a positive result — or just simply confused about what’s going on? Call your healthcare provider. They’ll be able to provide you with more details and, if you’re truly pregnant, they’ll likely schedule you for a prenatal visit (either via telemedicine or IRL) between 8 and 10 weeks.