How Common Is A False Positive Pregnancy Test And What Causes It?

Home Pregnancy Tests

The best way to get accurate results when using a home pregnancy test is to wait until your period late. At that time, the level of hCG in your sytem will be large enough that all of the pregnancy tests on the market will be able to detect it, producing a positive pregnancy test result.

Most women, who are trying to get pregnant, prefer to find out as soon as possible. That “two week wait” becomes unbearable. There are many home pregnancy tests on the market that claim you can test much earlier, usually 4 or 5 days before your period is due. These early test pregnancy tests are typically about 97% accurate, when all the instructions are follow exactly and you read the results within the time frame listed in the instructions.

What Can Cause False Positive Pregnancy Test Results?

A truly “false positive” test result, due to a faulty home pregnancy test is fairly rare. A positive result which is not repeatable, with subsequent home pregnancy tests, is usually because of one of these reasons: Chemical pregnancy, missed reaction time, chemical interference or an evaporation line on the pregnancy test.

Chemical Pregnancy

As unfortunate as it is, about 25% of all pregnancies end up being a chemical pregnancy, also known as an early miscarriage. A chemical pregnancy happens when a pregnancy is lost shortly after implantation. With the advancement in sensitivity of the home pregnancy tests on the market today, women are able to detect pregnancy in the very, very early stages. This is the downside of the super sensitive pregnancy tests – the joy of discovering pregnancy very early on, followed by crushing heartbreak if an early miscarrige occurs.

Missed Reaction Time

You really need to follow the instructions included with your home pregnancy test exactly. The manufacturer lets you know how long you should allow the test to sit before interpreting the results. If you let the test sit for longer than the instructions state, any results you interpret need to be considered invalid. Reading after the recommended time frame has passed can show results that you will misinterpret as a positive result.

Chemical Interference

If you are undergoing fertility treatments and have had a hCG (Human Chorionic Gonadotropin) trigger shot, you will need to make sure the shot has had enough time to metabolize through and clear your system. Fertility doctors suggest waiting about 14 days for your system to be clear of the hCG before taking a pregnancy test. Testing before this time may very well likely produce a positive result when you are not truly pregnant.

Evaporation Lines

Some pregnancy tests can leave an evaporation line on the pregnancy test, as the urine crosses the result area. The evaporation line is usually a very faint, grayish line in the results area of the pregnancy test. The color of the line is not what the test instructions say should be there, for a positive result, but many women, will erroneously interpret the line as a positive result.

If you feel you are having early pregnancy symptoms and not getting the results you think you should be from your home pregnancy tests, you should contact your doctor for a blood pregnancy test.

  • PrayinMama

    Not nessecerily no… You could have been pregnant but had a miscarriage things like that you need to see a doctor

  • H

    My last period started on May 23rd, 2014 and I haven’t had one since! I took a test today, and it was a positive! My boyfriend and I are very, very excited!
    However, the only thing that I am worried about is my existing health issues… I have a prolactin secreting pituitary brain tumor. I was diagnosed with it last year. I just hope that it doesn’t effect my pregnancy!

  • Vickie B.

    Congratulations! As you have a diagnosed medical condition, you will want to get your doctors involved as soon as possible for your health and your baby’s health.

  • Amy

    Same is happening to me, I have Hashimoto’s, which also makes it difficult, but I got a positive yesterday (3 days before due period), 2 negatives today.

  • moanie14311

    I was due my period yesterday my last period was 2nd of July. I did a test tuesday night witch came up with a very faint second line, the other was a clear 2nd line. I went to the walk-in-centre this morning due to having brownish like discharge stuff that looked the same as I’d normally get before my period. Any how i gave the doctor a urine sample and she did a test there and it came up negative and couldn’t explain to me why the other two i took where positive. Shes suggested having a blood test done by my gp. She also said that this has happened before and the person had a positive back from having bloods took. I cant help but think she was just sayin that to reassure me but I’ve lost hope now. It really has broke my heart because we did tell close relatives :(

  • Steph

    I recently took an at home pregnancy and the line was very faint so I waited until the morning and took the other one from the box and still got the same faint line. I decided to wait a couple of days and test with a more expensive brand name of clear blue and it said i was pregnant and gave me a 1-2 week digital answer. The following day I went to the doctors to confirm since I am 2-3 days late on my period and the results came back negative. I am so confused I don’t understand how I could have gotten 3 false positives at home and a negative at the doctors…help explain please!?

  • Vickie B.

    Unfortunately, you could have had an early miscarriage if your period did come fully on. If not, a blood test is definitely recommended.

  • Vickie B.

    I don’t think you got a false positive. It could be that the level of hcg in your system is lower than what the blood test could detect. It’s also possible that the lab that tested your blood just did a bad job of the test. That does happen sometimes. Until you get your period or the pregnancy tests come back totally negative, I wouldn’t give up hope.

  • JG

    On Saturday, August 9th I took two Clear Blue digital tests and both came back as positive. On Sunday evening, August 10th, I took another digital test that came back negative. Thinking that I had a chemical pregnancy, I took just one more yesterday (August 11th) and it came back as “pregnant 1-2 weeks”. Then I took one more this morning (August 12th) and it came back as negative again. I thought these digital tests were supposed to be 99% accurate??? Anyone have any advice or experienced this before?

  • Vickie B.

    It could be that the levels of hcg in your urine are on the very low level. The Sunday evening one could be that you had enough liquid in your system to dilute the hcg to a level that didn’t trigger the test. Are you testing before your period should have arrived?

  • JG

    Yes, all of these tests were before my period should have began. I usually have periods every 35 days, today is supposed to be the start of my new period – I’ve had just a tiny bit of spotting though so far…still feeling nauseous, slightly out of it, and with sore breasts. My nipples have also started changing (some strange goose-like bumps appeared). I had some bloodwork done yesterday and should hear back tomorrow. All of these test results have been like an emotional roller coaster!

  • Pip

    I have taken two home pregnancy tests that both said positive. I think I’m am due my period next week, but I am terrible at remembering these things. It might be this week. Everyone keeps telling me that it could just be elivated hormoan and not to get carried away. I definitely feel different but just very confused. Has anyone else experienced this?

  • Pip

    I have taken two home pregnancy tests that both said positive. I think I’m am due my period next week, but I am terrible at remembering these things. It might be this week. Everyone keeps telling me that it could just be elivated hormoan and not to get carried away. I definitely feel different but just very confused. Has anyone else experienced this?

  • Jennifer Dexter

    I’m about to take a pregnancy test. I was on birth control, but I have been off it for many weeks and I have not gotten my period. I just recently had a baby. She is three months. I wanted to wait to have anymore children. We definitely cannot afford another baby. But I don’t believe in abortion. I guess in the next hour we will see what God has in store for me:

  • Jennifer Dexter

    Its NEGaTIVE!!!!:-)

  • Vickie B.

    Typically, if you have a positive pregnancy test, you will be pregnant. You can’t have elevated hcg (the pregnancy hormone) unless you are pregnant.

  • kvanb

    I took two test which came out positive but when I took the doctor’s test at a teen clinic. I got a negative.
    Could the doctor be wrong?

  • Vickie B.

    There are a couple of possibilities. 1) The lab who ran your blood test did a poor job. 2) Your hcg levels are extremely low and fall below a “positive” result for the lab. If this is the case, you should continue to have positive pregnancy tests. 3) You had an early miscarriage. If this is the case, the positive pregnancy tests will stop as the hcg clears your system.

Last modified: February 14, 2014