One Pregnancy Test is Positive and the Other is Negative

Are you currently trying to get pregnant? If so, you have likely taken a home pregnancy test, or maybe a few tests, throughout the trying to conceive process. It can be confusing when two pregnancy tests show different results – one positive and one negative. Many questions come up when this happens. Is the second test faulty or is it something else entirely that we should be looking out for? What does it mean when one pregnancy test is positive and the other is negative? In today’s blog post, we will discuss what could cause two at-home pregnancy tests to have seemingly contradictory results, and how best to move forward in these uncertain circumstances. Read on for more info!

What Causes a False Positive Pregnancy Test Result?

There is no denying that the moment you think you may be pregnant can be both exciting and incredibly nerve-wracking. The first thing you probably want to do is take a pregnancy test!  You may want to take a pregnancy test as soon as possible or you may be someone who wants to wait until after your missed cycle to take a test. Either way, you expect the results to be accurate so you know as soon as possible if you are pregnant!

A false positive means that the test detected the presence of the pregnancy hormone human chorionic gonadotropin (HCG) in your body, even though you are not pregnant. This can happen for a number of reasons including:

  • Taking fertility medications with HCG 
  • Having had hormone therapy that contains HCG 
  • Having an ovarian cyst 
  • Having an early miscarriage, ectopic pregnancy, or other early loss of pregnancy 
  • A faulty test 
  • Using two different tests that detect different amounts of HCG

One of the most common causes of a false positive test is residual HCG left over in your urine from a previous pregnancy. This can happen if you went through a loss and your levels did not get back down to zero before you took a test. If you went through fertility treatment and used a trigger shot, it is also possible you still have HCG in your system.  The trigger shot contains HCG, meaning you would test positive until it leaves your system.  

False positives can also be caused by other factors, including certain medications and medical conditions, as well as user error when taking a urine test. There is also the chance that you may have taken an expired test or used one that was not stored properly. While these occurrences are rare, they can happen and it is important to know what to look out for.

Indent lines and evaporation lines can be mistaken for a positive test result. Typically, an indent line will be lighter than a true positive line. It will not have the same color intensity as the control line.  A faint evaporation line will look similar to a positive result but the second line will not change color like a true positive would. An evaporation line is actually just the urine sample drying on the test and it does not indicate that you are pregnant.

No matter what the cause of the false positive result, it is important to remember that a home pregnancy test should never be considered 100% accurate. It is always best to follow up with your healthcare provider for a blood test to confirm the results.  A urine pregnancy test will tell you there is a presence of HCG in your body. A blood test will tell you the amount of HCG in your body.  By taking two or more blood tests at least a couple of days apart, your healthcare provider will be able to track if the HCG is rising or falling.  This will confirm if you are indeed pregnant.

What Causes a False Negative Pregnancy Test Result?

False negative results can be more common than false positives.  A false negative occurs when the test says you are not pregnant even though you are.  There are a number of reasons you may get a false-negative result.  The most common cause is taking the test too early, before your body has had time to build up enough HCG hormone in your system.  

A false-negative pregnancy test can also occur when the test was not done correctly or if the instructions were misread.  You must follow all directions for using home tests and read the results in the time frame given.  Be sure to always check the expiration date before using any type of pregnancy test at home.

Other potential causes include using an expired pregnancy test, drinking a lot of fluids prior to taking the test, which can water down the HCG levels, and testing too late in the day when your urine is not as concentrated.  The best time of day to take a test is typically with your first morning urine.  This often gives the most accurate results in the early weeks of pregnancy.

It is important to remember that home pregnancy tests are not always 100% accurate and if you think there is a chance that you may be pregnant, it is best to follow up with your healthcare provider for a blood test to confirm a pregnancy. 

A woman lays on her stomach and looks down at a pregnancy test she holds in her hands.

How to Interprete Mixed Results on a Home Pregnancy Test

When it comes to taking a home pregnancy test, seeing mixed results can be confusing and leave you wondering what to do next. There are a few things to keep in mind when interpreting mixed results. 

First, it is important to understand that home pregnancy tests detect the hormone HCG. This hormone is typically only present in a woman’s urine stream if she is pregnant. However, factors such as taking the test too early or missing instructions can affect the accuracy of the test. The most accurate result would be the first day of your missed period or later.  Remember, with a pregnancy test, even a faint line means it is positive.  This is different from ovulation test kits in which both lines need to be the same level of darkness.

If you are using two different brands of tests, it is likely that one brand is more sensitive than the other.  This means the more sensitive test will detect HCG earlier in pregnancy than the other.  If you have taken two tests and one was positive while the other was negative, it is possible that you took the second test too early for it to be accurate.  Certain brands, such as First Response, claim to be able to pick up the lower levels of HCG in your body.

In cases such as this, it is best to wait two to three days and take another at-home test. This should give enough time for HCG levels to rise, which should provide a more accurate result. If you have a late period or are past when you expect your period to start, checking with your doctor is the best way to get answers.

If you are concerned about your results or the accuracy of the test, it is always best to contact your healthcare provider for further advice and testing. They can help provide clarity in uncertain situations.

What Else Can Affect Pregnancy Test Results?

Polycystic Ovarian Syndrome (PCOS) can affect a woman’s fertility and can lead to inaccurate results. PCOS is an endocrine disorder that causes small cysts to form on the ovaries. This affects hormone production and can interfere with ovulation. Due to this, many women with PCOS do not have regular ovulation or a regular menstrual cycle.  Thus, they may not know when they ovulated.  They may not be taking the test at the right time, leading to a false negative.

A chemical pregnancy can also cause false results on a pregnancy test. A chemical pregnancy is when a fertilized egg does not fully implant in the uterine wall and is lost shortly after conception. Since this loss occurs before most women would know they are pregnant, the hormone HCG may not have had enough time to be detected by either blood or urine tests. You may also receive a faint positive test, followed by a negative test a day or two later.  This is because the HCG hormone levels are likely falling due to losing the pregnancy.

There are typically two types of pregnancy tests including those that use pink dye and those that use blue dye.  The pink dye tests tend to give a more accurate reading than the blue dye tests.  A pink dye test will show a positive result if even the faintest line appears, while a blue dye test may need to have more definite blue lines for it to register as positive. This is why it is important to read the instructions on any at-home test and compare results between similar tests.

With these various factors at play, it is always best to follow up with your healthcare provider whenever you get unexpected or confusing test results. They can help provide clarification and next steps on what you should do next.

A woman sits on a couch and looks down at a pregnancy test she is holding in her hands.

In summary, when results from a home pregnancy test are mixed or inconsistent, it is a good idea to consult your health care provider. Professional tests are reliable, accurate, and will give the best results when it comes to determining a pregnancy status.  Mixed or inconsistent results on a home pregnancy test can be confusing and stressful, but understanding the possible causes behind them can help provide clarity.

It is important to remember that home pregnancy tests are not always 100% accurate and if you think there is a chance that you may be pregnant, it is best to follow up with healthcare provider for further testing and advice. It is also essential to consider that other factors such as polycystic ovary syndrome (PCOS), chemical pregnancies, and the timing of the test may all have an effect on the accuracy of results. Everyone wants the same thing, which is to have a healthy pregnancy!  Hopefully with the advice above, you will be able to understand how false positive results and false negative results can occur, so you know how to interpret them. 

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