How Does a Home Pregnancy Test Work?
- If you think you are pregnant, you may want to test yourself at home with a home pregnancy test. You can buy test kits at a drug store without a prescription. Home use kits measure a hormone called human chorionic gonadotropin (hCG) in your urine. However, these tests are qualitative, and the results are either positive or negative for pregnancy.
- The most sensitive test of pregnancy is best performed by a laboratory using a sample of your blood. These tests not only detect human chorionic gonadotropin (hCG) but also can indicate the amount (quantitative tests) of the hormone, which doubles every 2-3 days during the first several weeks of pregnancy. These more sensitive tests can tell you approximately how long you have been pregnant and even detect specific problems with the pregnancy. Your doctor can perform this test.
- Initially, many women prefer the privacy, convenience, and quick results from home test kits. Home pregnancy tests are not as accurate as blood tests done by your doctor. They also cannot determine if your pregnancy is developing as expected.
- The hormone hCG may be detected in urine about 2 weeks after conception (when the egg is fertilized by sperm).
- With the home test kit, you place a drop of your urine on a prepared chemical strip. It usually takes 1 or 2 minutes for the strip to indicate the result.
Home Pregnancy Test Preparation
To get the best results from your home test kit, follow the instructions that come with the kit.
- Read the label and instructions carefully: Review all instructions and pictures to make sure you understand how to perform the test. The instructions will tell you the following information:
- What the test is for and what it is not for
- How to collect and store your urine sample
- When and how to run the test, including timing instructions
- How to interpret the test results
- What might interfere with the test results
- The manufacturer's phone number if you have questions
- Only use tests regulated by FDA: Ask the pharmacist how you can know if a home use test is regulated by the FDA. If a test is FDA approved, the US government has not determined the product to be reasonably safe or reliable.
- Follow all instructions: You must follow all test instructions to get an accurate result. Most home tests require specific timing, materials, and sample amounts. You should also check the expiration dates and storage conditions before performing a test to make sure the components still work correctly.
- Keep good records of your testing.
- Call the 800 telephone number listed on your home use test kit if you have any questions.
- When in doubt, contact your doctor: All tests can give false results (meaning the test indicates you are pregnant when you may not be, or the test says you are not pregnant when you are). You should see your doctor if you believe your test results are wrong or to confirm the result.
Don't change medications or their dosages based on a home test without talking to your doctor.
During the Home Pregnancy Test Procedure
For most home pregnancy tests, you either hold a test strip in your urine stream as you urinate into the toilet or you collect your urine in a clean cup and dip your test strip into the cup. If you are pregnant, most test strips produce a colored line, but this will depend on the brand you purchased. Read directions carefully to interpret the results. Read the instructions for the test you bought and follow them carefully. Make sure you know how to get accurate results. The test usually takes only a few minutes.
- Some tests are able to detect low levels of hCG, indicating pregnancy. For the most reliable results, test 1-2 weeks after you have missed your period. There are some tests for sale that are sensitive enough to show you are pregnant before you miss your period.
- You can improve your chances for an accurate result by using your first morning urine for the test. This urine has accumulated in your bladder overnight. If you are pregnant, it will have more hCG in it than urine collected later in the day.
- If you think you are pregnant, but your first test was negative, you can take the test again after several days. Because the amount of hCG increases rapidly when you are pregnant, you may get a positive test on later days. Some test kits come with more than one test in them to allow you to repeat the test.
- The home pregnancy test and the urine pregnancy test used by your health-care professional are similar. Both can detect hCG, but your provider is probably more experienced in running the test. The doctor may follow up with a more sensitive blood test to see if you are pregnant and may conduct a physical exam for a more reliable result.
Types of home use test kits
- The most common kits use a test strip or dipstick, which you hold in your urine stream as you urinate into the toilet. With other tests you may urinate into a cup and dip the test strip into the cup. A section of the strip changes color if hCG is detected, indicating that you are probably pregnant.
- Some kits contain a urine collection cup with a built-in testing device. You either put a few drops of urine into the device or immerse the device into urine in a cup. Again, a test strip changes color, showing positive or negative for pregnancy.
Other, less frequently used test kits require you to mix urine samples with powders or liquids. The chemical reaction produced shows a color change, which you compare to a chart for interpretation.
After the Home Pregnancy Test Procedure
If you are pregnant, you will want to follow up with your doctor to confirm the result and begin prenatal care. If you are on any prescription medications, do not stop taking them without first consulting your doctor.
Home Pregnancy Test Risks
There are no medical risks associated with testing for pregnancy.
You may obtain inaccurate results that are either falsely positive or falsely negative. Errors can result depending on how you collect the sample. You may be too early in pregnancy for the hCG levels to be high enough to confirm pregnancy. If the urine is not collected the first thing in the morning, it may be too dilute to return positive, even if you are pregnant. Medications may cause the test to give an erroneous result
One study showed that women had difficulty following the instructions on the package insert. In this study, many results returned negative in patients who were subsequently determined to be pregnant.
Home Pregnancy Test Results
The accuracy of the home pregnancy test depends on how well one follows the instructions and interpret the results. If you mishandle or misunderstand the test kit, you may get inaccurate results.
If the test is performed too early in the menstrual cycle, the hCG levels may not be high enough to produce a positive test result. This may be a particularly significant issue if one has irregular cycles or is uncertain as to the date of onset of her last menstrual period.
When to Seek Medical Care
If your period is late and you suspect you may be pregnant, wait 7-10 days before trying the home pregnancy test. If the test is negative, wait a few more days. If you still don't menstruate, try the test again. If you still test negative and your periods do not return to normal, see your
For More Information
If your symptoms don't seem to agree with your test results, or if your test or device does not seem to be working properly, you can report it to FDA's MedWatch program at the US Food and Drug Administration, MedWatch.
If you want to notify the Office of In Vitro Diagnostic Device Evaluation and Safety of the US Food and Drug Administration directly of a problem with a home use test, send an email to [email protected].