False negatives and false positives on pregnancy tests aren't common, but they are possible.
There's a lot riding on a pregnancy test. It may be the most life-changing test you'll ever take – which means you're counting on an accurate result. Unfortunately, pregnancy tests can sometimes be wrong.
While home pregnancy tests are generally very accurate, there are lots of ways to get a faulty result. Often, this is due to making common testing mistakes.
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A "false positive" pregnancy test means that the test displayed a positive result when you're not actually pregnant. A "false negative" pregnancy test means the displayed result is negative when, in reality, you are pregnant.
Can you get a false positive pregnancy test?
It's possible to get a false positive pregnancy test, though it's unlikely.
Pregnancy tests check for the hormone hCG in your urine. When the embryo starts to implant in the lining of your uterus, as early as six days after conception, cells that will later develop into the placenta begin to produce hCG.
Because pregnancy tests are very good at detecting hCG, "false positives are quite rare," says Emily Holthaus, M.D., a board certified ob-gyn who specializes in the care of high-risk pregnancies. (She's also a member of the BabyCenter Medical Advisory Board.)
Why would a positive pregnancy test be wrong?
"Unless the test is completely defective for some reason, a positive result usually means that there is some hCG in your urine," says Dr. Holthaus.
If you don't have a viable pregnancy, hCG may show up in your urine for one of several reasons:
1. Very early miscarriage
Sometimes called a "chemical pregnancy," a very early miscarriage can cause you to have a positive pregnancy test result shortly followed by your period. An embryo forms and might even implant in your uterus, releasing enough hCG to be detected on a very early pregnancy test. The embryo then stops developing, often due to a genetic issue, leading to miscarriage.
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In most cases, you won't even realize you've had a chemical pregnancy. But if you test before or around your expected period, you might get a positive result.
2. Ectopic pregnancy
When a fertilized egg implants outside of the uterus, it's known as an ectopic pregnancy. This almost always occurs in the fallopian tubes, which can become blocked due to inflammation. Certain health conditions, such as endometriosis and pelvic inflammatory disease, are linked to an increased risk of ectopic pregnancies.
Although ectopic pregnancies result in a positive pregnancy test, they're never viable – meaning the embryo can't develop into a fetus.
At first, women having an ectopic pregnancy experience the normal early signs of pregnancy (such as nausea, vomiting, fatigue, and breast tenderness). Signs and symptoms of ectopic pregnancy appear later, such as vagin*l bleeding or spotting and pain in the abdomen, back, shoulder, or neck. Pain may be dull and throbbing or sharp and shooting.
If you had a positive pregnancy test but suspect you might have an ectopic pregnancy, see your healthcare provider right away or go to the emergency room. Ectopic pregnancies are a medical emergency: As the embryo grows, it will cause the fallopian tube to burst, leading to potentially life-threatening bleeding. A doctor can diagnose an ectopic pregnancy with an ultrasound and treat it using medication or surgery.
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3. Molar pregnancy
A molar pregnancy is when cells that would normally become the placenta develop abnormally, forming cystic tissue and making it impossible for the pregnancy to continue. You're more likely to have a molar pregnancy if you have a history of several miscarriages, if you have fertility problems, or if you're under the age of 15 or over the age of 43.
Similar to an ectopic pregnancy, women having a molar pregnancy may at first have normal pregnancy symptoms. But within the first three months, they'll experience vagin*l bleeding and pelvic pressure or pain. A doctor can diagnose a molar pregnancy with ultrasound and remove the molar tissue with surgery.
4. Menopause
Women who have gone through menopause can sometimes have elevated hCG levels that are detectable on a pregnancy test, even though they're not pregnant. If you're not sure whether you're pregnant or in menopause, check in with your doctor.
5. Certain medications
Chemotherapy medications can make your period stop, and certain tumors can produce hCG even when you're not pregnant. This can falsely lead you to believe you're pregnant.
You can also get a false positive result if you test too soon after taking a fertility medication that contains hCG. If you're undergoing fertility treatments, be sure to carefully follow your provider's instructions on pregnancy testing.
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6. Other rare medical conditions
A number of rare medical conditions can cause hCG to be present in your bloodstream. These include gestational trophoblastic disease (when a tumor forms instead of an embryo), certain tumors, liver disease, and some rare genetic conditions, says Dr. Holthaus.
It can be really hard to get a false positive pregnancy test result, especially if you've been actively trying to get pregnant. If it's helpful, remind yourself that pregnancy loss is very common, impacting an estimated one in four pregnancies. Most women go on to deliver a healthy baby.
Can a blood pregnancy test be wrong?
Yes. Blood pregnancy tests done at a doctor's office tend to be even more sensitive than urine pregnancy tests done at home. Blood tests measure the amount of hCG present in your blood rather than just giving you a simple positive or negative result. But they're not infallible.
"Blood pregnancy tests can have false positives for the same reasons urine pregnancy tests can be wrong," says Dr. Holthaus. Also, in rare cases, certain proteins present in some people's blood (known as heterophilic antibodies) can cause a false positive result on a blood pregnancy test.
Can a negative pregnancy test be wrong?
Yes. False negative pregnancy tests are much more common than false positives. They're usually due to user error, so be sure to follow the instructions on the test packaging.
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If you test too early in your cycle (generally speaking, before a missed period), you're more likely to get a false negative. You might also get a false negative if you use an expired pregnancy test or one that was stored improperly.
To avoid a false negative, test first thing in the morning, especially if it's right around or before a missed period. "HCG, and urine in general, is more concentrated when you first wake up in the morning compared to later in the day," says Dr. Holthaus.
What to do if you have a surprise positive pregnancy test
Dr. Holthaus recommends confirming your result by taking another pregnancy test, and then contacting your doctor or midwife to discuss scheduling an appointment.
