What Can Cause a False-Positive Pregnancy Test?

It is rare but possible to have a false-positive pregnancy test. A recent miscarriage or abortion, certain medications, and several other conditions may cause a false-positive result.  Pregnancy test kits detect human chorionic gonadotropin (hCG), a hormone that starts to rise when a sperm fertilizes an egg. This hormone helps your body maintain the pregnancy. Though they are about 99% accurate, pregnancy tests are not foolproof. 

This article explores several reasons you may get a false-positive result on your pregnancy test. It also discusses which tests are more accurate and how early you can take them. Lastly, this article answers some frequently asked questions about pregnancy tests. 

Several conditions may cause a false-positive pregnancy test. 

An ectopic pregnancy is a real pregnancy that will return a positive pregnancy test; however, the pregnancy is nonviable, meaning it cannot result in a live birth. This type of pregnancy occurs when a fertilized egg implants in an area outside the uterus. One of the fallopian tubes is a common area for an ectopic pregnancy to implant. If you have an ectopic pregnancy, you may notice symptoms such as severe, sharp pain on one side of your abdomen, vaginal bleeding, or dizziness.

An ectopic pregnancy can be a serious emergency for the pregnant parent if the growing embryo ruptures the fallopian tube causing severe bleeding. See your medical professional as soon as possible if you suspect an ectopic pregnancy.

Learn more about ectopic pregnancy.

After a miscarriage or abortion, the hCG hormone may remain in your system for up to 6 weeks. This may lead to a false-positive pregnancy test. 

If your miscarriage was spontaneous, tissue might remain in the uterus. You will likely notice that you continue to have vaginal bleeding. A procedure called dilation & curettage (D&C) may be necessary to remove the tissue inside the uterus.

Let your medical professional know if you had a spontaneous miscarriage as they may need to assess you. 

Learn about the signs of miscarriage. 

Certain fertility treatment medications may cause a false-positive pregnancy test. The following drugs are synthetic hCG injections which will cause a pregnancy test to appear positive:

• Novarel
• Profasi
• Ovidrel
• Pregnyl

It is a good idea to wait at least 7-14 days after your last injection before taking a pregnancy test.

When a fertilized egg cannot implant completely in the uterus very early on in the pregnancy, it will still produce detectable amounts of hCG. Chemical pregnancies are common but typically go unnoticed as the egg passes during menstruation. 

It is best to wait a week after your missed cycle to take a pregnancy test because it may lead to a false-positive pregnancy test.

Learn more about chemical pregnancy. 

Evaporation lines may show up on your test after your urine completely evaporates, usually within 10-30 minutes. Reading the test after the recommended time may cause you to mistakenly believe you are pregnant. 

Be sure to read the directions for your pregnancy test and follow them according to the manufacturer’s recommendations.

Often, people may attempt to take a pregnancy test but may not perform it correctly. If the urine is too diluted, it may not give an accurate response. It is best to take the test first thing in the morning. 

Check the expiration date and read through the directions. Set a timer when it is time to wait for the results and read them according to the recommended window of time.

Learn more about the best time to take a pregnancy test. 

It is rare, but certain conditions may result in a false-positive pregnancy test. These include:

• ovarian cysts
• ovarian cancer
• chemotherapy
• kidney disease
• urinary tract infection
• pituitary disease
• molar pregnancy

There is always a chance that you may have a false-positive pregnancy test. However, the chance is small. Most home pregnancy tests are almost 99% accurate.

Some home pregnancy tests are more reliable than others. Urine hCG tests are most reliable about a week after your missed period. A pregnancy test in your medical professional’s office may use a blood test. Blood tests can detect smaller amounts of hCG, confirming pregnancy earlier than a urine test. 

You can use an at-home pregnancy test on the first day of a missed period. However, keep in mind that the earlier you take the test, the harder it is for the test to detect hCG. Some sensitive tests may be accurate even before you miss a period. Blood pregnancy tests can also detect hCG earlier and more accurately than a urine pregnancy test.

Here are a few common questions about false-positive pregnancy tests. Tahirah Redhead, MPAS, PA-C, MPH, has reviewed the answers.

A false-positive pregnancy test can occur when you have a severe urinary tract infection. These results are due to the high amount of white blood cells, red blood cells, and nitrates in your urine.

Sometimes you may have a fertilized egg that has not attached to the uterus lining. This embryo will continue to produce hCG as long as it is in your body, but it will not develop into a fetus. These eggs then pass during your menstrual cycle.

Certain infertility medications and medical conditions can cause hCG levels to rise in your body and give you a false-positive pregnancy test.

It is relatively rare but possible to have a false-negative pregnancy test. The most common reason for a false negative is that you took the test too early. The earlier after a missed period that you take a home pregnancy test, the harder it is for the test to detect hCG. Even if your period is late according to your typical cycle, you might have ovulated later in the month.

Pregnancy tests detect the rising level of hCG hormone. This hormone rises when an egg is fertilized. Most of the time pregnancy tests give accurate results. However, there are rare circumstances when you may get a false positive. 

Certain complications with implantation of a fertilized egg such as an ectopic pregnancy, chemical pregnancy, or recent miscarriage may cause a misreading. There are also certain medications taken for infertility that cause elevated hCG without a pregnancy. There is also the potential for user error when taking a pregnancy test.

If you get a positive pregnancy reading, let your medical professional know, as they will want to assess and monitor your well-being.