What causes a positive pregnancy test

A pregnancy test can show a false positive. Although this is a rare occurrence, this most frequently happens with home pregnancy tests due to errors when using it or due to expiry.

Another common cause for a false positive is a chemical pregnancy. This occurs when the egg has been fertilized, but is unable to properly implant on the uterine lining. It is unable to develop into a full fetus, but the body initiates the production of hormones anyway, giving the test a positive result. A pregnancy that does not continue however will eventually show a negative pregnancy result. 

In addition, many women who undergo fertility treatments with hCG injections will often see false positives, as well as women who unknowingly have tumors that produce hCG. 

Main causes of false positive tests 

Changes in test results generally occur when the test has expired, and therefore it is very important to confirm the expiry test before using it. If the expiry date is correct, other reasons for a false positive may include: 

1. Test done incorrectly

Before using a home pregnancy test, be sure to read the package instructions. Pay attention to the time necessary to read the result, as some test results may change after a set time. 

In addition, before using the test, you should cleanse the genital area with water, as some soaps or creams can impact the test results, and show a false positive or false negative. 

Learn more about how to take a home pregnancy test. 

2. Chemical pregnancy 

This type of pregnancy occurs when the egg is fertilized, but the embryo is unable to implant into the uterus. In these cases, the body will start to produce hCG hormone, and therefore it will be detected in the urine or the blood. However, because the embryo fails to implant, it will eventually lead to a miscarriage, which can be confused for a late period. 

3. Use of some medications

Some medications used for fertility treatments contain high quantities of hCG. This hormone is what is identified in pregnancy tests, which can lead to false positive soon after a treatment. 

Other more common medications, like anticonvulsants, diuretics or tranquilizers can also cause changes to the final result. Therefore, it is important to read your medication pamphlets before completing a home pregnancy test, or to complete a blood test in the lab for more accurate results.

4. Health problems  

Although this is more rare, a false positive can also occur with some illnesses. This can happen, for example, with tumors that produce hormones, like breast cancer or ovarian cancer. 

Read about causes of false negative pregnancy tests. 

How to prevent a false positive 

To prevent a false positive result, it is important to follow the instructions as outlined in the pregnancy test package. After the test, you should also: 

• Repeat the test 3 to 5 days later 
• Do not reference your results after the indicated time 
• Book an appointment with your doctor within the next month 

The best way to prevent changes to your result is to complete an hCG blood test, as there is less room for error with this test method. Read more about the advantages and disadvantages of different pregnancy tests. In addition, before the test, the doctor will be able to evaluate whether there are any medications or health circumstances that can alter the results. 

Pregnancy tests hold a lot of weight. With one positive test, your entire life will change. But what about when a test comes back falsely-positive? A false-positive test result only happens less than 1% of the time, but when it does, it can make the following days or weeks confusing before you realize you’re not actually pregnant.

So what actually causes a false-positive test and how do you decrease the chances of it happening to you? We’ll cover the top reasons for false-positive pregnancy tests below, but if you’d like to learn more about how tests work, click here.

False Pregnancy Test Results

In some cases, tests offer a false result. But, in other cases, they detect the presence of an embryo, even if the pregnancy is not viable. For the first five points below, we’ll cover false results where the test detects elevated hCG (the pregnancy hormone) and indicates a pregnancy that does not exist. The final two points, we’ll cover instances when the test accurately detects hCGs in a pregnancy that is not viable.

1. You Had A Miscarriage or Abortion Recently

After an embryo implants , it begins to secrete human chorionic gonadotropin (hCG), the pregnancy hormone. HCG is produced by the cells surrounding a growing embryo. The presence of hCG triggers a positive test result.

After an abortion or miscarriage, hCG levels start to go down  over the a period of 9-35 days. If you take a pregnancy test within this window, you can get a false-positive result because the test is still detecting the pregnancy hormone and can’t tell that the levels are decreasing.

2. Some Medications Can Trigger False-Positives

If a woman is having a hard time getting pregnant, her doctor may put her on fertility treatments. Some of those medicines include hCG which helps follicles release mature eggs within a woman’s ovary. If a pregnancy test is taken within 7-14 days after fertility treatments, a false-positive can occur. It is recommended to delay pregnancy testing until 1-2 weeks after the last injection or treatment.

Tell your doctor if you’re taking any medication because various medicines can trigger false-positives. Once your physician knows what you’re taking, he or she  can help you with over-the-counter test results.

3. Medical Conditions Are Sometimes to Blame

Sometimes medical conditions can trigger a false-positive in urine tests. If you have any of the following, they might inflate your hCG levels and you might get a false-positive:* Ovarian cysts* Kidney disease* Urinary tract infection* Pituitary problems

* And in some cases, ovarian cancer and other serious diseases

If you get a false-positive test result and have ruled out other causes, consult a medical professional to test for these conditions. Your doctor may recommend a blood test to get a more accurate test result.

4. Confusing Evaporation Lines

If the pregnancy test instructions were not followed precisely, sometimes an evaporation line can be mistaken for a positive. Many tests show two lines when hCG is detected and one line when hCG isn’t detected, or a plus or minus sign.

For the line tests, sometimes, a faint-colored second line appears. This may represent an early pregnancy or may simply be an evaporation line.

If you read the test after the recommended time in the instructions, the results might be a false-positive since the evaporation line may show up more clearly. Avoid any confusion by following the test’s timing directions exactly as they’re written. Each test brand has specific instructions, so follow them closely.

5. User Error

Like most consumer goods, pregnancy tests expire and are sometimes used wrong. Using a test incorrectly or using an old one can lead to a false-positive result. Here are a few tips to avoid user error:

* Before using your test, check the use-by date and follow the instructions closely.* Use the tests when your urine is concentrated like when you wake up in the morning. Diluted urine from excessive water-drinking can affect the accuracy of the test.* Avoid using a test too early in your menstrual cycle.* Leave the dip-stick in your urine stream for the exact amount of time required by the instructions. Set a timer to keep track.

* Set another timer to check your results in the correct time frame outlined in the instructions.

Technically-Positive Pregnancy Test Results

The next two points are unique in that they indicate the presence of BhCG in the body so they are technically accurate in giving a positive result. However, an ectopic or chemical pregnancy sadly is not viable.

6. An Ectopic Pregnancy

When an embryo implants itself outside the uterus , it’s known as an ectopic pregnancy. Almost all ectopic pregnancies—more than 90%—happen in a fallopian tube. As the pregnancy grows, it can cause the tube to burst (rupture). A rupture can cause major internal bleeding. This can be a life-threatening emergency that needs surgery.

Even though the embryo isn’t viable it will still produce hCG, triggering a positive pregnancy test.

If you think you have an ectopic pregnancy, or have a positive pregnancy test paired with severe pain on one side of the lower abdomen and spotting, seek immediate medical help as soon as possible.

7. A Chemical Pregnancy

A chemical pregnancy is a miscarriage that happens before week five of the pregnancy when an embryo implants in your uterus but it never takes hold. The loss happens so early that you may not even know you're pregnant. However, the embryo produces hCG and can cause a false-positive on a pregnancy test. This situation is known as a chemical pregnancy.

Chemical pregnancies aren’t a result of action or inaction by the woman but can occur because of:* Fibroids* Scar tissue* Low amounts of certain hormones like progesterone

* An irregular-shaped uterus

The emotional strain from false-positive results can be severe and mentally taxing for you and your family. We recommend waiting to use at-home pregnancy tests until one week after the expected start of your period.

We also recommend getting a confirmed diagnosis at a local clinic or with your healthcare provider. You can always book a 30-minute appointment for a free pregnancy test at The Source clinic nearest you. Click the button below to schedule a free appointment today.