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Even though your home pregnancy test might boast that it’s practically foolproof, there’s always a chance that the results could be off. Occasionally, it’s possible to get a false positive — where a test says you’re pregnant even though you aren’t.

False positives are less common than false negatives, where a test says you aren’t pregnant when you actually are. But they can still sometimes happen.

So if your test reads PREGNANT but you still doubt the results, take a look at this list. Here are 9 reasons why false positives can sometimes happen and what to do if you think you’ve got one.

At-home pregnancy tests typically work by testing your urine for a pregnancy hormone called human chorionic gonadotropin (hCG), which starts increasing rapidly after an egg is fertilized.

If the test picks up hCG in your urine, the result will read positive — that you’re pregnant. If no hCG is detected, the result will read negative — you’re not pregnant.

Most OTC pregnancy tests claim to be right up to 99 percent of the time. But there are a number of things that can potentially make them less accurate and give you the wrong result.

So what kinds of things can confuse your pregnancy test and cause it to erroneously give you some life-changing news?

Here’s a look at the most common causes:

You took the test too early

Pregnancy tests are most accurate when you follow the manufacturer’s directions exactly.

Though it can be tempting to take one the second you suspect you might be pregnant, it’s better to wait until a full week after your missed period. (Feels like an eternity, WE KNOW.) Tests are less accurate when taken before that, which means you could be more likely to get a false positive or false negative.

You had a chemical pregnancy

Chemical pregnancies happen when a fertilized egg is unable to implant or grow. The pregnancy is lost super early, and most women never even realize they happened.

But they can cause the body to start producing hCG, which could get picked up on a pregnancy test and cause a false-positive reading.

Chemical pregnancies are common and often occur for no reason. But they’re an important reason why it’s worth waiting at least a week after your missed period to take a pregnancy test: Holding off that long will reduce the chances that you get a false positive from any hCG that’s still in your system.

You have an ectopic pregnancy

Ectopic pregnancies are pregnancies that occur when a fertilized egg implants itself somewhere outside of the uterus — like one of the fallopian tubes, the cervix, the abdomen, or the ovaries.

These pregnancies aren’t viable because an egg can’t thrive and grow outside of the uterus. But early on, they can still cause the body to produce hCG and lead to a false-positive reading.

You might have an ectopic pregnancy if your test reads positive but you’re experiencing sharp waves of abdominal or pelvic pain, sharp pain on one side of your abdomen, spotting or bleeding, dizziness or fainting, or pressure in your rectum.

If you notice any of these symptoms, seek medical help ASAP. Ectopic pregnancies are health emergencies and they can damage your reproductive system if untreated.

You recently had a miscarriage

The body’s hCG levels start to drop back to pre-pregnancy levels after a miscarriage, but it doesn’t happen overnight. HCG can be detected in a woman’s blood for up to 6 weeks after a pregnancy loss.

So, if you were to try again to conceive shortly after a miscarriage, it’s possible for a test to pick up hCG from your previous pregnancy and give you a false-positive result.

You recently had an abortion

Abortions can cause subsequent false positives for the same reason that miscarriages can.

It can take up to 6 weeks for the hCG from your previous pregnancy to clear out of your system. So if you were to try again to conceive shortly after having an abortion, your test might read positive by mistake.

Your test showed an evaporation line

Some pregnancy tests use two lines to show a positive result (and just one line to show a negative one). The lines are usually bright blue or bright pink, but the second line can occasionally be faint.

Sometimes a faint second line can mean that you’re pregnant. But it can also just be an evaporation line — a meaningless line that forms after your urine has evaporated completely. Especially if the line is totally colorless.

Following the test’s directions to the letter can help you avoid evaporation lines. But if you really want to steer clear of this potential debacle, just pick a different pregnancy test.

Some digital tests use readouts like “Pregnant” or “Not Pregnant” instead of lines, which research shows are less likely to get misinterpreted.

You’re on fertility meds

If you’re undergoing fertility treatments, your doctor might prescribe a synthetic hCG trigger shot like Novarel, Pregnyl, Ovidrel, or Profasi. These shots prompt the follicles in your ovaries to release an egg, but they can also cause an OTC pregnancy test to give you a false positive.

This is especially likely to be the case if you take the test too early. Again, it’s another really good reason to hold off testing for a full week after your missed period.

You’re on other meds

Fertility meds aren’t the only drugs that could potentially mess with your test results. Other meds, too, can affect your hormone levels and potentially cause a pregnancy test to read positive by mistake.

Some common culprits include:

  • anti-anxiety medications, like diazepam (Valium) or alprazolam (Xanax)
  • antipsychotics, such as clozapine or chlorpromazine
  • anticonvulsants, like phenobarbital or other barbiturates
  • Parkinson’s disease medications, including bromocriptine (Parlodel)
  • diuretics, like furosemide (Lasix, Diuscreen)
  • methadone (Dolophine)

If you’re on one or more of these drugs and are trying to get pregnant, talk with your doctor. They can help you figure out the best steps to take to help you get an accurate test result, a safe pregnancy, and a healthy baby.

You have a medical condition

In addition to certain drugs, some medical conditions can also affect your hormone levels and potentially mess with your pregnancy test.

These include:

In rare cases, ovarian cancer or pituitary problems can also affect pregnancy test results.

Okay, so you took a pregnancy test and it says you’ve got a baby on the way.

Whether you believe the results are legit or you suspect they might not be, your best bet is to make an appointment with your OB-GYN.

They’ll retest you in their office (either with another urine test or a blood test) to tell for sure if you’re pregnant. From there, if your result is indeed positive, your doc can help you make a plan of what to do next.

Until then, just remember to breathe and take it one step at a time. Feeling like you got a false-positive result on an OTC pregnancy test can be stressful, but answers are right around the corner.